Alright, once you get to her last pokemon, switch out into Noivern and use light screen. Noivern will most likely get OHKO'd by it, so you can safe switch into Meowstic and use Light Screen. Then try and get Will-O-Wisp and replace it for Shadow Ball or Dark Pulse to widdle it away as you're attacking it. I used this with the help of Smok3iT on my own thread.