I feel your pain. I worry about my mom and my significant other a lot as well as myself. It's normal for us to do that. But as always, we can't live anyone else's lives for them.
I'm not quite clear on whether her eyelid was drooping or twitching, but a twitch is something that happens to everyone at some point or another, and drooping eyelids are a natural part of aging. If that's all she's got going on, I wouldn't be too worried. (Well, I WOULD be, in your shoes, because like you, I have health anxiety and go to the worst possible scenario. But there's probably no need to be worried, is my point.)