I think it’s such a misconception that exercise makes you lose weight. I’ve been through my own journey losing like 3 stone and it’s honestly like 90% the calories you eat. There is literally no point torturing herself trying to run when she can barely even walk. It’s not going to get her anyway. At her size with no exercise at all, her metabolic rate will be so high, even around 2500 calories a day would be a decent deficit to lose a few pounds a week