Is her whole body affected? Animals can get epilepsy too and other neurological disorders that cause shaking, convulsions, tremors, etc. It could be a few things. If it's just her head/neck and just in response to water splashing, that's an inherited spasm triggered by water that we bred into them.
If it's her whole body, check all water sources and food sources for heavy metal and toxin/chemical contamination, and if you think it's heavy metal toxification, feed her raw apples, seeds and all, and look into other heavy metal detoxifiers to see what you feel ok with giving her, as there are a few herbs and fruits and vegetables that detox heavy metals; unpasteurized apple cider vinegar with the 'mother' in it should also do the trick. It's the pectin in apples that detoxifies them.
She may be eating lead paint from somewhere, as they often mistake the flakes of old paint for calcium sources or minerals. She could have some parasite or disease affecting the brain. Try to see if anything in specific always happens before a seizure, that could help pinpoint what's going on.
Best wishes.
