Im sorrry to hear about that. i am in the same boat as her my metabolism is shot for the exact same reason and it used too be so fast. just support her as best you can, and it would help to see a nutritionist so she can still keep healthy eating habbits and get in to shape. also taking vitamins help allot, exspecially b vitamins they should help here metabolism function a tad bit more. she should try lifting weights, and trust me she wont get huge and bulky like she may think from lifing weights. i wish her the best.
Does she still have help,therapy? I would advise her to talk to them,they can help her with losing weight healthy and/or the worrying about it.lily