Hi. I don't see how it could really contribute much to weight gain. What product is it, and what is she eating it with? Is it a sugary protein powder? Was she basically eating an extra meal just to have some?

I use collagen powder off and on when I know I'm just not getting enough protein overall, and/or when I'm trying to heal inflamed joints/muscles/tendons. When I take it, it's added to things that I'd be eating anyway: the 'au jus' or sauce of whatever meat I'm cooking, a soup, maybe some SF jello... and my weight has been very steady for the last 4-5 years. Collagen is found in meats, particularly in the joints and 'icky' bits. If you consume a lot of broth, if you regularly eat ribs or chicken wings, if you like the 'sinewy' parts of any kind of meat, you're probably already getting lots of collagen. So unless there's something weird about the product she's using or how she's using it, I really don't see how it causes fat gain.