... Wait s%@& Inquisitors get invisibility?! I must have confused them with Warpriests!
Well, the plan is already heavily laid out and she's starting her journey into her tails being a floofy pillow. More invisibility castings is always a good thing, and she can make better use of a scaling charm person later that doesn't drop off horrendously. That, and she already gets her own invisibility at 9th level. She won't be able to multiattack + feint until endgame, so she's going to need all the invisibility she can get.
Maybe buy an invis ring?
Also, if you want to play catch up with Spellcraft, all you need is a reliable way to Detect Magic (such as an item or a permanency spell), and you're good to go to id magic items as well. Investigators get free inspiration with Spellcraft iirc.