Musts: A halfblood must have a high concept indicating their parentage (Daughter of Athena, Son of Ares). The Big Three (Zeus, Poseidon, and Hades) are forbidden to PC's

Makes sense, Also I see where you're going with restricting the big three. Have you thought about bringing things from the  series following Percy's? Also I think it'd be cool to have a Prophecy or Quest as a Must too. Don't know if that would be fair, to restrict two of the Half-bloods Aspects, but still.

Inhuman Recovery [-2], Inhuman Toughness [-2], The Catch (Weapons of the Old World (swords, daggers, bows, etc.)
Options: abilities based on their parent to be determined with gm consent upon creation)
Minimum Refresh Cost: -6

Is the base -6 to ensure they get some other powers or a miscalculation?

Inhuman Strength [-2], Inhuman Recovery [-2], Inhuman Toughness [-2], The Catch(piercing weapons)

I get that we don't want to make them a heavy refresh but no Inhuman Speed? (never watched the show that much so assumption time) Wasn't Buffy/Slayer made to be physically comparable to Vampires and Demons? without speed she's lacking in a crucial area.

Minimum Refresh Cost (-5)

Notes: If a player wants to play a Whedonverse vampire they mUST have a HIGH CONCEPT ASPECT that explains their having free will. This may be taken only be taken with the GM’s approval

Honestly my only issue here is that by virtue of their refresh they have free will. Even for the lowest level game "Feet in the Water" (6 refresh) Perhaps this template could just represent the Free Will having Hellmouth vamp?
Additionally you could add/bump up their current powers and grant them the "Gifted With Soul" Power from the custom power list.

Gifted With Soul [+1]
Description: You are different from other Red Court Vampires. Normally your kind do not have a soul, for it is antithesis to your being, and destroyed once you have had your first killing feed. You however have somehow managed to store your soul in an item, making a phylactery of sorts.
Musts: You must be a red court vampire, must have an aspect that reflects this power.
Effects:
Silence the Beast. You loose your Echoes of the Beast power. As a Red Court Vampire with a Soul your beast is suppressed by the morals other Red Court Vampires lack. You are reimbursed for the refresh cost of Echoes of the beast, since you no longer have it.
Refresh Bonus. You have somehow maintained your soul, keeping free will. Add +1 to your refresh level.
Phylactery. Your soul is stored in an item that you must keep on your person at all times. If it leaves your person, you loose the above benefits, becoming an NPC. You may spend one fate point to give you one days time to retrieve the item.
Altered Catch. You are no longer burnt to a cinder in sunlight, but you are weakened in it. In sunlight your catch is automatically satisfied for any attack. In addition add a new condition to your catch: "Phylactery Damage."
Made Whole [-1]. If you take this upgrade your soul no longer resides in your phylactery, which becomes a mundane item, it has been restored to your body. You loose the "Phylactery" portion of this ability, and the "Phylactery Damage" condition on your catch.

linky:
http://www.jimbutcheronline.com/bb/index.php/topic,19934.0.html
Also couldn't think of a way to tangent to this but, you should totally have the Mist from the Olympian world. Not sure how really but it was so cool.

I think one could only be aware of the spell on them if they were a magically attuned individual.
I'd say Lore if the "princess" has any magic.
Conviction if she is aware of the spell.
Discipline other wise (will save from D&D is my thought here).

Quite the contrary.  You obviously bruised your ribs while diving for cover in a desperate bid to avoid that fireball - a bid that was successful, but that came at a cost.

^Yup. I find it fun thinking of unique tie in consequences. With things like this particular scenario it seems to paint a better picture (at least for me).

The original question though: I'd say "B" or "C", personally leaning towards "B". But if your casters are concerned with that many shifts, "B" is where I'd go. "A" is too close in shifts to "C" to make a difference for me, and "C" seems to quick and easy. Additionally, Are they not worried about the 3rd and 4th Laws? 'Cause all three scenarios breech those Laws. IMHO

So we are going to be starting a new game soon and the majority of players are mostly unfamiliar with the Dresden files.
What I was wondering is what the fine folk of the forum think the key points of the Dresden-Verse are. And to what depth to cover what areas.
It makes sense that not every player would need to know about the laws of magic, but it seems that they should all have a rudimentary understanding of the different Vampire courts and the Fae. I'm just not sure what that should include.
Are there any summaries of the Dresden-Verse I could hand out?

It's also important to note how she carries the coin. If you attempted to take it from her by force would you need a surgeon? Because Harry has knocked some of the denarians out and lifted the coin. And if you have a less scrupled character the method with Cassius and the bat could go over well too. Though you probably wouldn't want the child there. Either way though, If your insincere about your death threat chances are the denarian can figure it out and then your kinda stuck. The circle sounds like a really good idea, it may be cool for the wizard and the child of the denarian to go through his/her family's secrets to get articles to better bind the circle with. (aspects for free tagging). But man this is a tough situation, props to your GM for it!

It seems to me that the rule for making a block persistent should work the same for these. so a 12 shift affect over 4 rounds, plus 2-4 for duration would be a 20 ish level effect.

Well if you're able to get 12 shifts reliably with Evocation than by all means, thats the power level your working with. But, blocks with rituals are wards, technically not different but thematically wards have to be stationary or anchored. I was considering that you literally have 4 separate instances of a simple action at 12 shifts, with a duration of a scene costing 3 (random # between numbers I gave)
so

12*4=48+3=51 shifts of complexity.
this ritual would let you use simple actions (examples were stealth, alertness, investigation, and athletics) at 12 shifts four times in the scene.

Anyways, as was already mentioned those rules were for evocation and it sounds like that was the initial problem. Blocks and simple actions created with Thaumaturgy cant be extended in the same way. But, I think its a choice for the GM and the group. If this is the kind of power level the group feels is appropriate for a caster then it makes since to do it that way. If everyone feels like it may be to powerful then alter it to something less then, I still think the multiple aspects would be the best option.

Thats close to what I was planning on doing. I absolutely love the note card idea, stolen lol. Thank you both.