I would shy away from giving LEGAL advise.

My reaction to your question would be that IF your aesthetician SPECIFIES in the "qualifications" or "capabilities" or "services offered" that she doesn't provide her service to males, then she would be (in my opinion) safe and NOT discriminating. Similarly, you can't require a plumber to fix your electrical device. It's outside their expertise or field of services offered.

If, however, she ADVERTISES that she provides her services to everyone, then if she turns down a male customer because he's male, then there's a problem. IMO

Similarly, if the plumber offers "Plumbing and Electrical Services" and won't fix your electrical device because you're a male, then there's a problem. IMO

This is only my opinion and NOT offered as legal advise.