I'm sure it's been discussed at some point but she is obviously The Cailleach, amongst other things.

Here's my latest take on the Power structure for the Dresdenverse.  It breaks down as Aspects of Reality.  Here, an Aspect is Reality itself, whereas an Avatar is the faith/belief manifestation of that Aspect.

EVERYTHING
In the beginning, there was EVERYTHING.
From sheer boredom, EVERYTHING then split into two:  Order, and Chaos

ORDER

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- Order is vast, with varying degrees of permanence. 
 - The center of Order is Reality.  It is where everything is governed by strict Laws.
 - The rest of Order is the machine-works of Reality.  It is governed by the same Laws, only of varying degrees.
 - Order has Aspects, which are manifestations of its properties.
 - Order consists of two Pantheons of Law: Divine Law, and Natural Law
    - Divine Law is what Must Be, to keep Chaos from Order.
    - Natural Law is what Is, to make Order of Chaos.
       - Divine Law has Eternal Aspects, which serve its purpose.
          - Archangels, Angels, and Divine Beings of other mythological pantheons belong to Divine Law.
       - Natural Law has Eternal Aspects, which define its purpose.
          - Spirits and Elemental Beings belong to Natural Law.

CHAOS

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- Chaos is vast, with no rhyme or reason.
 - The inner edge of Chaos is The Outside, which lies outside of Order.
    - The Outside has some semblance of Order, in order to interact with it.
 - The rest of Chaos is Empty Night, which is endless disorder and chaos without light.
 - Chaos has its own Aspects, which are manifestations of its properties.
 - These Aspects of Chaos exist only 'near' the border with Order.
    - The Higher Aspects of Chaos are the Old Ones, ancient powerful beings.
    - The Old Ones are served by Outsiders, which attack Order to restore Chaos.

ASPECTS of ORDER

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- An Aspect is the Manifestation of the Purpose of a Law.
 - A Divine Law exists as an Absolute, without change or compromise.
   - As it is Absolute, an Aspect of a Divine Law is Immortal, Unchanging, and Unbending.
 - A Natural Law exists as a product of Order, which is constantly in motion and change.
   - As it is Malleable, an Aspect of Natural Law is influenced by faith and belief in Reality.

The Concept of Natural Aspects

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- There is Gas
   - There is Air
     - There is Wind
       - There is The Air Stream
         - There is The Hurricane
         - There is The Storm
         - There is The Gale
         - There is The Breeze
         - There is The Calm

The Breeze is a small part of the sum of Air.  It is unaware of its place in things; it only knows of its own existence.  It is an Aspect of Air, but it is a separate manifestation of it.

Further, the Breeze is eternal, as long as the Wind blows.  But humanity experiences the Breeze, and names it Aura.  With faith and belief, Aura is manifested.  She appears human, and thinks somewhat like a human.  But she is an Avatar of the Aspect of the Breeze.  She is not the Breeze itself, only a part of it.  In a very small way, she is a part of the Wind as well, but only as the Breeze is part of the Wind. 

Aeolus is the name given to all Winds.  Thus Aeolus is born, as an Avatar of all Wind.  Aeolus encompasses Breezes, but is not an Avatar of the Breeze; it is both greater and lesser than Aura. 

The north wind is named Boreas, and thus is the Avatar Boreas created through faith and belief.  Boreas is separate from Aeolus, but is an Avatar of the Aspect of the greater Aspect.  He is weaker than Aeolus, but more powerfully defined in his own domain.

Applying it Loosely to The Winter Queens

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Mother Winter is the Avatar of Winter.  She is the bitter cold, the death of crops, the creep of ice, the fall of snow, and the dark of long night. 
Winter Queen is the Avatar of Air and Darkness.  She is the freezing wind and the dark of long night.
Winter Lady is the Avatar of the Cold Tundra.  She is the icy plains.
Winter Knight is the Avatar of Winter's Hunger.  He is the barren stores and desperate measures.

Each is an Avatar of an Aspect of Winter.  The lesser mantles encompass fewer Aspects.  Thus are they weaker.  Winter's Hunger might seem more powerful than Cold Tundra, but it is dependent on life to suffer, whereas the Cold Tundra only requires cold and water.  One is desperate and rash to act, whereas the other is not.

Applying it Loosely to Hecate

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Mother Earth is life and death, summer and winter, joy and pain.  Mother Earth is the earth, the air, and the seas. 

Humanity looks upon Mother Earth, and gives her the name Hecate.  Hecate is born, becoming the Avatar of Mother Earth.  She is part of Mother Earth, but not all of it.  Hecate is aware of herself, and her role.  She is all-encompassing of the experiences on Earth.  And she recognizes a threat from Outside.

Mother Winter is an Avatar of one of Hecate's Aspects.  But she is not Hecate.  Nor is Mother Summer.  But all six Queens of Faerie combined are Avatars equal to the sum of the Avatar Hecate.  Thus are they Hecate, but they are not.  They know that they are Avatars of her Aspects, and recognize their role in Hecate's existence.

Why we'll never see Hecate

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Hecate is above and beyond human perception.  As she is every Aspect of Mother Earth, she is nearly equal to Mother Earth itself.  Thus is she unable to manifest there.  The Mothers' too are great in scope and power, to the point that they can but rarely manifest on Earth.  To do so would to encompass all that they are in a very small piece of Reality; they are not ALL of the Aspects of Winter or Summer, as they are but Avatars; but they are enough of them to damage Reality with their presence.  The Queens are less, but they too can warp reality; thus are they there sparingly.  Only the Lady and Knight encompass small enough Aspects that can be manifested on Earth. 

   

Epic.
So, if I understood you, the reason we won't see "Earth" is because metaphysical "weight" would have to great an effect on reality?  Like a magic black hole?

http://www.jimbutcheronline.com/bb/index.php/topic,41981.0.html.  10/22/14

This should be a no-brainer.

I'm so there
 

I don't know?  How about:  " your friendly neighborhood occult shop?"   

Pick up the "Dictionary of Angels" its got some great stuff.

I know this is a sore subject for many of us in the UF fandom, but LKH (Ms. Hamilton) has written some of the best work in the genre.  At least up until Narcisuss in Chains.  Try her first novel: Guilty Pleasure's. I would suggest not skipping around with her work since the tone of the books have changed greatly and she no longer writes "jumping on point" novels for the Anita Blake series.  Tanya Huff is also very good at her work and I do enjoy the Kim Harrison novels.

 What aspect of the genre do you like most?  The mystery? the magic or the relationship?  These are the three pillars of the UF landscape and most authors tend to lean on one more that the other.  (i.e.  LKH's Merry Gentry series which is ALL magic and sex and has NO mystery aspect whatsoever). 

Jim Butcher is one of the few authors out there that has been able to maintain a good balance of all three after more than a few books.So many others only use the "mystery" as a plot device to futher the magic/shipping aspects of the series, which is IMHO a rather poor and lazy effort on the part of many ape LKH's success in the field as the reigning author in the genre.   (She's the most well paid but he's probably the best he is at what he does)   But Jim's the only one I've heard of who know exactly how many books he's going to write AND has an overarcing storyline.

Ok, I'm going to stop rambling now.  Hope my stint on the soapbox helps you out.

Just put a glossary in the back of the book.  It worked for Jordan and Herbert.