Thank you all very much for your input on this matter. It has been very stressful for all of us, because as most of you know, turtles can become a part of the family. Lucy is actually a turtle that I rescued from someone's home, because they had her in a plastic kiddie pool on their back porch, and they were calling for below freezing temperatures all week long after sunset, and nobody even thought about bringing her inside. So I brought her in and took care of her, and the owner was so grateful not to have the *hassle* anymore, that she gave her to me. That's been almost two years ago, and this is the first incident we've had with her, and it's a whopper.
Also, to Steve, I appreciate everything you've said, and while I know this isn't a good substitute for veterinary care, I am in touch with an exotic animals specialist at our local vet's office here in town, so I'm helping her keep tabs on Lucy's progress, as well as letting her know of any changes. We correspond by phone as well as via email, where I send her pictures of Lucy and her eyes every other day. Unfortunately, we live in a very small town, so her area of expertise is very limited when it comes to RES, but she's been a Blessing as well.
All of the help is very, very much appreciated. It is indeed a bad situation for this poor slider, but I believe that what goes around, comes around. The main thing is that Lucy is no longer anywhere near her, and she is out of harms way.
On a positive note, Lucy has been a lot more active this morning, instead of just the frantic thrashing around at the sides of her tank. She's been keeping her eyes open a lot more. I had read on the page about enticing them to eat, about soaking some pellets in tuna water, so I tried that last night, but she only ate three or four bites. BUT in a situation like this, every little bit helps, and at least it's progress!
I can't thank the people who made and maintain this site enough, as well as all of the members on this board for your support and advice!