I'm going to the gym with my very overweight friend.
Are you making her go to the gym? Does that sound like something nice to do?
I don't care. She needs to lose weight.
It's nice you want to help your friend, but it's bad to push people into things they don't want to do. They will be even less likely to do them out of resentment.
Ugh, honestly I just want to spend more time with her and make sure she loses weight.
If she doesn't want to do it, then you should find different and healthier ways to have her lose weight. You could offer to go on walks with her?