Teenage daughter that will only wear leggings or extremely loose sweat pants

I have a 16 year old daughter that has struggled with the way things "feel" her entire life. She goes through phases where she will try new "styles" but always reverts back to only black leggings from one particular store or very baggy black sweat pants. She refuses to even try any other clothes. Not sure what to do. One part of me feels like she should at least be willing to try other pants since at times she has worn other things but part of me feels like that is mean.

I believe wholeheartedly that this is a "real" issue and just want to help her the best way I can. I have concerns about her adult life if she cannot learn to overcome some of this. She is in therapy for anxiety and depression but is not doing any OT.
Thanks