Thanks to everyone for your kind words. I've been trying to find out about this type of thing, and I did find an article on seizures, convulsions and tremors in reptiles. From what I've read these appear to be tremors, not seizures, since she's not losing consciousness. I have some hope that way, because tremors are often related to a dietary deficiency, or exposure to some toxin.
Seizures, Convulsions And Tremors In Reptiles - Veterinarian Practice & General Health Issues
So I'm going to overhaul her diet. I'm fairly certain my nightcrawlers are safe, but the salmon I've used is Pacific salmon, which could honestly come from anywhere, and maybe contain chemicals or something from whatever part of the world it was caught.Some places have very poor standards when it comes to pollution and chemicals in water and soil.
So (assuming she pulls through this) she's getting only fish (probably rainbow trout) from around here that I can be reasonably sure is safe.
I also must confess that I've never used vitamin supplements before, so I am going to do so from now on.
If she doesn't improve, then it is probably neurological or virus related, and there isn't much I can do anyway. But as usual, I will remain positive, and hope for the best.