I think Slayers would have basically all the Inhuman Powers (Strength, Speed, Toughness, Recovery) add some form of vampire sense and something to represent the remnants of the memories of former slayers, and your'e done on the powers side.
The actual power that Buffy displays in the Series varies a lot, but these are all in line with what can be seen there.
Any other abilities are represented by skills and stunts.
High Fists and Weapons or maybe the "Armed Arts" Stunt, and high Athletics.
Add decent Alertness and you more or less have the required skills finished off.
The rest can be used to actually make a Character, and not an Archetype.
Catch... dunno, afaik Slayers have no catch. So it would have to be +0.
There is this one episode in season 3 ("Helpless") where she looses her powers, maybe what happens there can be used as a catch. But it would still be +0.
"A Slayer" is not Buffy.
When i comes to powers, then "A Slayer" is Buffy. Buffy would have loads more points of refresh to buy stunts, and more skills than a newbie-Slayer, but power wise they are all more or less the same.
I'm talking tv series Buffy here... The comics are another thing altogether.