They are 7-8 years old and have been eating the following diet for the last 6-7 years.
Mixture of Green Leaf, Romain, Boston lettuce, Radiccio (sp), zuchini (sp), regularly.
Carrots once a week
Occasional green grapes
Reptomin every other day
Earthworms twice a month
Live feeder fish very rarely
Tank water temperature is in the mid 70s, basking area has a heat lamp, UVB
I left some uneaten lettuce in her tank last night. After the lights went out she eventually came off the dock at around 1:00 AM and ate it.

She ate all her reptomin and a little lettuce this morning also and seems more active. I have to think that's a good sign.
I'm not sure what the white stuff is. She IS shedding a little on her neck. So at first I assumed it was loose skin. I've seen that plenty of times. But when she wasn't acting the way she usually does, sneezed a couple of times, and lost her appetite I started panicking. When I looked at it closely when she was on the dock it looked a little foamy as opposed to skin. So I started thinking it was coming out of her mouth, but it's impossible to be sure.
I have a very small apartment and no other tank to separate them.
I'll keep a close eye on her and if I see anything else I'll report back immediately.