Did you try resettling her? I know you say that you can't, but we didn't used to be able to resettle x and now we can even if he has slept for 1.5h so it is worth trying to resettle her in the hope that one day it will work!
Hopefully she will still manage to get to bt at 6.30, though - I know that x would be able to after that nap, so I will keep my fingers crossed for you.