Yeah like for being 6' 2" it has me as almost overweight, which I know in reality I am not even close (my guess would be I'm ~13% body fat), so BMI, isn't really the best thing. Personally, I'd say if you have a good relationship with her try to include her in activities you do whether that be hiking, playing soccer, going on runs, etc etc you'll build companionship (which is always nice to have later on and stuff) as well as give her a taste and development of the enjoying exercise.