Random, your account angers me at your therapist four ways--
-Use of the scolding word presentable, the scornful parent at its worst. I doubt she'd tolerate you using that tone with her. A real power thing.
-Her continuing the power play by asking the leading question --which isn't a question at all-- why you're embarrassed. If one wants someone else to feel it ease they DON'T point out their embarrassment
-By drawing the false analogy about her dress compared to yours. She's a professional, doing a job. You're the client. That kind of faux "argument" is domineering in my opinion.
-Her discounting your reporting you'd be unconcerned with her clothes.

If she sincerely believes that dressing up might make her clients feel better, there are so many more tactful ways to impart that opinion.