Though it's at least a 3 shift effect (4 if the Aspect's Sticky)

Not necessarily.  The book doesn't quote a difficulty for placing aspects on yourself, but it does say "an unopposed manuever roll is pretty easy."  Now, if I were the GM adjudicating this I'd probably call it a 1 shift effect since there's really nothing to overcome (it makes her less likely to make noise while moving, it doesn't affect anything outside of her character). 

As for making it sticky... I'd call that up to the user.  The whole "minor effort of will" thing Harry uses to end his effects, it exists as an aspect until she dismisses it.

Personally I'd say that any time a supernatural being breaks an oath sworn on their power it would twist one of their aspects, potentially even their high concept.  If the character eventually makes good on the oath, or is released from it somehow, the aspect could be changed back or more likely changed a second time to reflect the character's growth in the interim.

And as a personal note: How would you "stat" a Black Court Scion (aka: Dhampir)?

How would they ever come into existance in the first place?  Blampires are dead.  Squick factor aside, I'd think they'd be incapable of sexual procreation.

Now, I can imagine some sort of ritual, ala Buffy, to essentially steal some of the power from a Blampire's demon and infuse it into a mortal, for later use against other members of the black court.  You could treat them like Scions in that the powers are heritable and similar to their supernatural "sire."

I never really considered giving mortal spellcasters fate points for not killing people with magic given that the "taken out" system gives total control (witin reason) of the defeated character's fate to the victor.  A compel is worth a fate point when it complicates a character's life, and since the character in question is free to engage in the conflict with all of their magical might there really isn't much of a complication.

On the other hand compelling a character with the appropriate aspects to turn that knock out blast into one that will spatter a hated enemy all over the wall is something I'd do.

Honestly I, as a GM, would allow a character with the Focused Practitioner (Biomancy) to buy the various Inhuman Whatever powers, with the fact that said practitioner has spent years tinkering with his/her body and reinforcing it with magic.  A good catch for toughness/recovery powers would be magic, as magical attacks could disrupt the enhancements.

Think of anything that gives back Refresh as making certain kinds of Compels irresistable. That's probably the best way to look at it.

Then this should give Refresh back, since a BCV has no option to avoid taking damage from, say, being immersed in holy water.  The reason I'd say that this catch is worth a little more than others is the way it can be used.  Spraying entire zones with, for instance, acid risks harming your own people.  Dumping massive amounts of holy water around the place does not.  Additionally, a catch that prevents safe handling of some material, rather than simply permits that item to be weaponized for a normal attack is substantially more dangerous.

I’m contemplating a houserule to add potential to the catch.  See, some creatures (Black and Red Vampires are the most common) suffer actual damage from contact with otherwise innocuous substances, such as sunlight and holy water.  Other types of damage simply bypass their supernatural toughness/recovery powers, such as wooden stakes for the Blampires (to the best of my knowledge they are free to handle wood to their cold dead heart’s content.) 

My proposal: if simple physical contact with a normally innocuous substance (such as holy water or sunlight) causes damage, +1 to the value of the catch.  This would also apply to things like cold iron or silver if they cause stress through contact in addition to their usual use (getting turned into weapons). 

Also, having items that grant you power is basically saying that the GM will take them away some of the time.

...which is why you take the Thaumonuclear Deathzooka as an aspect silly, that way the GM has to really work to take it away, and has to pay you fate points if he does.

If one of my players actually called something the Thaumonuclear Deathzooka I'd be tempted to allow it.