Am I a bad friend?

So my best friend of 15 years has always been there for me through thick and thin. Some arguments here and there but they never lasted long and they were usually petty. She has psoriasis. Has her entire life. When we were younger, she said they(drs) considered it "moderate'' in severity. It never bothered me back then. Shes gone through a lot because of it (body issues, trouble finding employment, love issues) and I helped as much I could. But honestly, its absolutely disgusting. I hate it when she wears her hair up or wear tshirts and shorts(she rarely does unless shes known the person for years). When she sits on my couch my anxiety level goes up just because of it. And I understand why men wouldn't like it. I feel like telling her to cover up, and she would get less hate. But I feel like a terrible friend for even thinking that and I'm not sure I would even have the balls to tell her.. she would be devastated and just started wearing summer clothes again for the first time in years. The sun is making it better, but I wish she would tan at her house instead of when she comes for visits. How should I tell her without sounding horrible? Because I do love her to death.