Erm... It's hard to say. The Inquisitor system doesn't represent psychic potential very well. After all, Wp is a measure of control - not necessarily power. Number of powers represents versatility.
I'd say power potential probably comes under the powers you choose for the psyker. Choose formidable powers if they're supposed to be a powerful psyker, less so if they're not.
Ultimately, there is actually a lot to be said in favour of adapting the DH psychic system for Inquisitor.
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However, in this case, I'd advise something like perhaps Eta or Theta level - your descriptions make me perceive her as less powerful than I think of Maya Avens (who is a Zeta level, although towards the high end of that). You said you've read War of Shadows, so you should have some idea of the power level I give Maya.
She's not quite as powerful on the tabletop as she is in fiction - she's reined in for the sake of the game - but I personally think a Zeta-level psyker should be bloody scary.
Of course, others might have different opinions of power levels, so I'll look and see where the general consensus ends up.
