I am glad you sent a call out for good thoughts for Annie. Mine are being sent to her, you and her vet.
I've been thinking of what you said about her symptoms. It does sound like poisoning of some sort. Sometimes, when a dog has a flea bath and the flea killing stuff isn't duluted, this could hurt a dogs liver and kidneys, especially if the dog has a sensitive system due to age, etc.
My hope, since you've shared that she's doing better, is that it was something mild that she can get over. The IV will help dulute the gunk and help the liver and take stress off the liver and kidneys.
Since you aren't quite sure what she might have gotten into, I would ask that you do a good look around in your house, the garage, and front and back yards (trash area too) for anything that might still be lingering- I would hate for her to get better and go back to that horrible stuff.
Sending my best- OXOXOX