nothing wrong with the peanut butter, it's good for you if it's natural. My breakfast usually consists of a peanut butter sandwich on whole wheat break with a glass of milk.
for exercise, maybe running/swimming would be better than p90x. i have never tried the program, but I can only imagine that it would get boring after a month. If she sucks at running, start her at 20-30 minutes easy everyday (not on a treadmill). After she builds her endurance she can go 40-50 minutes. throwing in weight training/core work would be good too.
Hate to break it to ya, but legumes are bad for ya even if its natural. Though u can strip most of the bad stuff from beans when cooked right, not sure about peanuts but major brand peanut butter and even natural ones are a huge no no.
For the OP: http://altmed.creighton.edu/Paleodiet/Foodlist.html
general guidlines for what I said. I insist ye take a look over this list.
However, everyone's bodies are different. you could cut in some peanut butter and beans. just try to do what works for ya.
edit: cant believe i forgot. START HAVING UR GF EAT AVOCADOS. dont ask why, ensure u do this!!