I remember someone coming to my high school to give a pep talk.  He said to the boys "If you want to know what your wife will look like in 20 years...look at her mother."  In other words physical attraction only won't last into old age.
However, unless he is exaggerating, 80 lbs is a lot to gain in a couple of years and does seem like an eating disorder.  I would encourage her to ask for a referral to a clinical nutritionist to see what is going on.