My daughter had been putting on al ot of weight in the past year. Here is what happened

BEFORE(Jan. 2014):
Height: 5'4
Weight: 108 lbs.
Waist size: 28 in

AFTER(Dec. 2015)
Height: 5'4
Weight: 219 lbs.
Waist size: 45 in.

I am unsure of what to do. I have tried putting her on a diet, but it didn't work. She has been at her girlfriend's house a lot lately, and her girlfriend has also gotten very fat. I am completely stumped. I am worried that my daughter will influence my youngest duaghter's eating happits. My youngest daughter has already put on 40 lbs., so it might be to late. Please help me.