Please tell your therapist.
No point in going if you don’t
It’s nothing to be ashamed of stop acting like it is.
And noooo don’t show up dressed why put that stress on yourself.
I don’t think ( did not look) that you live your life going out dressed alot when you are asking about telling her.
Save that for later if that is what you want to do .
But please be real and please tell her it will help you.