You could just require that they do something genuinely worthy of vengeance.

Maybe a +3? That brings the weapon rating up to 4, enough for a Taken Out to most humans.

Still seems rather anemic. It's really just +1 stress, and in the likely event that the character has Guns > Fists / Weapons it's actually still worse than just firing the thing.

How about making the gun weapon 3 when used as a club, letting people swing it with Guns, and giving it +2 stress when ambushing?

More of one than the weapon rating?

Yeah. If there's no melee-enhancing Power, you're much better off firing the gun than swinging it. Even at an opponent who's within reach.

I feel like being able to just point at a thing and declare, "I'm getting through whatever toughness power he has, without needing to find out what his catch is," is worth refresh.

Oh, so the user gets to pick the target?

Then yeah, it should cost a fair bit. I was thinking that the designated target was pre-set by you.

[-1] Give’em an ‘Earp’: Wyatt Earp was as well-known for smacking people over the head as he was for shooting them -- when you pistol-whip someone with Earp’s Colt and land a successful attack, you also inflict the fragile aspect, “Stunned”

Not keen on this. Once you have the option of making a maneuver + attack, why ever do one orthe other?

In this specific case the fact that it's on a weaker method of using the weapon might keep regular attacks in play, but it still obsoletes many maneuvers. And this Power would be pretty terrible in a different context.

[-1] “No!”: Wyatt Earp was never shot, despite throwing himself into numerous gunfights, including a crossfire that should have had him dead to rights. You gain +1 to Athletics rolls to avoid gunfire. (Note: Am considering making this Inhuman Toughness with the catch of 'Anything but gunfire'. Cost will be the same)
[-1] “Justice is Coming”: As a Venator, Wyatt was well known and feared among supernatural enemies. That fear and belief extends to his weapon. If you spend a fate point, attacks from Earp’s Colt bypasses one level of toughness for the scene, i.e., a creature with Supernatural Toughness is treated as having Inhuman when attacked with the Colt.

These seem weak.

+2 to dodge bullets would be a fine stunt, and "only against bullets" is a pretty textbook +5 Catch. If you convert this to a Toughness Power, it could be Mythic for the same cost.

+2 stress to targets with Toughness Powers would also be a fine stunt, and would be pretty clearly better than that Power. Also, that flavour text made me expect an Intimidation bonus.

[-3] Pied Piper, Eat Your Heart Out: By playing Culein’s Flute, the user can entice people to follow them, or to run away, at range. The player gets a +2 to either Performance to create a temporary aspect on a person. If the player attempts to create an aspect on a zone, there is no bonus. The player decides which effect to inflict before rolling.

Three Refresh for a stunt?

1 Refresh is plenty for "+2 to single-target maneuvers aimed to make someone follow you or flee". If anything, that's narrow for a stunt.

[-4] Bardic Faerie Magic: Replaces Pied Piper. With training and attunement, Culein’s Flute offers the user magic sponsored by the bards of the wyldfae.
Benefits: The user can use Performance instead of Discipline, and Presence instead of Conviction, when casting spells. The caster also gets +1 to spell power when casting enchantments.
Item Slots: The user gets 4 Focus Slots, minus 2 if they already have either Evocation or Thaumaturgy. No focus slots if they already have both.
Agenda: Culein and the bards of the Wyld seek to enchant and seduce. They have an image to keep up, and wielders find themselves pulled toward such.
Evothaum: The user can cast certain Thaumaturgy spells with the speed and methods of evocation, such as Conjuration and Veils.

Seems alright.

[-1] The Devil’s Own Luck: Once per session, after rolling, you may freely reroll any number of your dice. However, using this takes a toll on the user -- immediately after the roll is resolved, Sin’s Charm hits the the user with a psychic attack equal to the roll’s total. Any consequences resulting from this attack must be aligned with whichever of the seven deadly sins closest matches the intent behind the action (i.e., attacking = Wrath; Rapport = Lust; pickpocketing = Envy, etc.). The user can use this effect again at the cost of one mental stress per use.

My experience with Demonic Co-Pilot makes me suspicious of this one. I can't say for sure that it's a bad idea, though.

[-2] Echoes of Many Beasts: Once per day, the user can declare what kind of beast the collar emulates. The user must wait until the next sunrise to change the animal -- and the animal type is reflected by a charm that manifests on the loop.

I like this one.

Go here: https://www.paranetonline.com/index.php/topic,53176.0.html

To be honest, I don't see the point. Speed powers fit the books pretty nicely, I think.

What supernatural things can she do?

There's no reason DFRPG can't have negative weapon / armour ratings. It never has, but they would work fine.

You could also change weapon and armour from deal and relationship to favourable and unfavourable conditions in general, but I'd prefer negative ratings.