I would be on my way to a lawyer's office.

I’m studying to be a massage therapist. Where was the rash? If it was on her leg then you could still treat her back. If it was on part of her back, technically you could treat around it and avoid that area. I know governing bodies are different in every area but it’s not “illegal” to treat a person with a rash. Treating on the rash itself is contraindicated but not treating entirely isn’t. With that being said, you are allowed to deny treatment if you don’t feel comfortable treating someone and your boss should recognize that. You could take legal action and site the standards of practice. Clients should also understand you’re human too but hey, people. Not everyone is understanding.

Not a massage therapist but many state and local laws on hygiene and disease control limit what a massage therapist or manicurist or hair stylist can do, because they’re worried about the spread of disease or parasites. What May be legal in one place May be enough to lose your license elsewhere.