It also sounds like she should be doing a lot of work with her insecurities. Is she willing to do that? Is she committed?
To me it sounds like her behavior stems from a lack of self-esteem. At least for me that kind of thing does.
Now the tricky part for you OP is that there's really not that much you can do to help her. You can be loving and supportive but it really is something that she needs to work on with herself.