Muscle dieases and herbal treatment

I have a question. I'm going to start writing a new story soon and in it, one of my MCS has a type of muscle diease. The problem? I can't decide what to give her. Cataplexy seems interesting (the sudden dropping/lost of muscle control is what intruges me most) but I've heard it comes as a side of effect of having narcolepsy, and I'd much rather not give her that. (Though not gonna lie, the image of her falling asleep while she rides a dragon does make me giggle in a morbid way XD). Does anyone know of any muscle dieases similar to cataplexy, or any muscle disease in general?

Also, this girl doesn't have much money (she was raised in a monastry) so her medication for this will probably be herbal. Does anyone know of any herbs good for lowering pain? Swelling (if any)? Or your all around basic herbal nessicaties any mage/monks would have with them? One of her good friends is an heir apparrent to a duke, so he would be able to chime in something medically speaking, but for the most part I see her gaining relief from herbs.

Thank you for all your help!

Umm, you have magic and dragons, so this isn't exactly our world - right? So why do you care if there are any plants in our world that could cure muscle diseases? And why care about mundane diseases at all?
It's your word, so you are the goddess to create the disease as well as the cure! Just don't make finding the cure too simple for your MCS.