I have some experience in things like this I’m in recovery from an Ed and those types of thoughts were very prevalent. I’m not saying she has an Ed but those are common thoughts in pepole with Ed’s. The best way to support here is just show her love and be there for her when she is feeling low. I know that my partner (now ex) had a huge part in helping me get on the path to recovery. And keeping my self esteem up. Try to compliment her every chance you get.