Can a coworker speculate about my health to a third party?

I found out a coworker was emailing my mom behind my back about my health. I have a chronic illness that I try very hard to hide. This coworker and I do not get along, so I try to hide my symptoms from her moreso than most. Regardless, she knows nothing about my illness and is not a Dr. My mom says nothing bad was said in the email, regardless it feels like a personal violation. When I asked my employer to speak to her, he said he would not get involved and I needed to address it with her myself... even though the emails were sent during working hours from a work computer, and the only reason she knows anything about my health is that we worked together... what can I do? This coworker is unreasonable towards me and I don't trust that she will stop just because I ask.