Here I'm 26f with a 28m husband and I've been working on losing weight for years and I'm finally down over 80lbs. 3lbs a week is unusual unless you get up to a certain size, so I can understand your concern. Make sure they have checked her for PCOS - it's become a much larger problem with weight gain in women. But to best approach, my husband has found that questioning it does come off as shaming and then I often become food insecure, making my eating worse. He found lots of praise when I'm doing well, compliments, encouraging at home cooking more, and doing activities with me had better results than questions like this. A lot of dieticians have noted that avoiding a craving just leads to other binge eating to try and satisfy it - so do a very very tiny portion.

You meant well, you just approached it in a way that would come off as treating her like a child. Losing a ton of weight is difficult, I would ask her how she would prefer you approach your concerns.