Hello T.,
Your daughter is now a teenager with all the doubts, problems and frustrations that come with her age. She has to accept her new body: she is becoming a woman and I'm sure you can remember how unsettling it was.
Now that you are reassured about her health, I would suggest not to mention her weight or appearance anymore. She is who she is, overweight or not. Don't make it more of a problem than it may already be for her.
Don't push activities on her that make her think that she needs exercise in order to lose weight. She may not be energetic but once again it's the age: they are tired all the time.
Ask her about any interest or passion she may have and want to pursue. She just needs to get out of her room, of her head, of herself and see that there are so many things to do in life, that she can be part of all that.
She reads, that's great but life is not only in books. Encourage her to take part in it too.
Once she finds other interests, she won't have time to eat anymore.
Please don't make her diet, take pills or exercise against her will. She just needs to establish a good relationship with food. Eating is a necessary energy for your body that should be pleasant to ingest, it's not something that you do out of boredom.
And don't forget to tell her how beautiful she is.
All the best
F.