corrections:
1. Is this sentence OK or how would you say it?
2. I mean she is fat and it is hard for her to do daily activities.
You could say it like you wrote it but that is kind of rude. Hahaha I don't think there is a polite way to say it though. Hahaha "She's so fat that she can't do anything." and "Her weight is out of control." are even ruder. Lol