Not sure to be honest as early days yet, but I'd check her brightness settings and also whether she lets the screen automatically turn off (i.e. through the auto lock feature), or whether she clicks it off with the top button. My OH's battery lasts about a day and it's because she has full brightness constantly and also just leaves the screen on all the time, waiting for auto-lock to actually put it to sleep. On the other hand, mine lasts 2 days minimum and I have brightness set way down to less than half (but still bright enough for everyday use) and I always click to sleep, rather than leaving the screen sitting there on doing nothing for 2 minutes at a time. Personally I think that's why I get a lot more out of mine.
Just a tip 🙂