My D is a senior now. She gained about that same amount of weight during her first two years. She then took up weight lifting as a way to feel more positive about her body. When she was home her dad would make comments about what she was eating, which of course she resented. I tried to avoid commenting, because she was on the alert for judgmental remarks. Eventually she joined the ultimate frisbee team and started running and now she’s lost most of the weight. It happened when she got motivated on her own. My feeling is that you should not bring it up unless she does, and even then just be supportive.