For passion your friend should work with Martial things. I suggest making a mojo bag out of some red fabric (or even just red felt or construction paper). In it I would put five each of five different herbs or stones associated with love, romance, and/or sex. She should find some appropriate herbs and stones on a correspondence sheet (we have articles on them, stores generally provide them, and they're in the back of every general/basic magick book) and just sort of go with her gut feeling when choosing specifics. When dealing with herbs she should obviously take into account allergies, and she should also consider how she and her boyfriend feel about their scent.
Bless the bag and keep it under the bed or between the mattress and the box-springs... or keep it in whatever other room they have all their passion in, I guess. I would suggest recharging it every two or so months with sunlight and moonlight, and I would also suggest replacing it every two years. At the very least you should replace the herbs and re-bless it.
Before I get to you and your wife, may I ask how open she is to the idea of getting back together with you?