OK, so you're soppy like me that's fine I understand
We had a sheep ate a tinsy bit of rhodedendron last year, she foamed at the mouth and via vet advice she still died 6 hours later, stressful to say the least. We'd just has her a week or so.
You seem quite calm about it so that's a good start, she is old and maybe it's her time. Can you phone your vet for advice rather than have a visit? Have a look around where she's been nibbling, they will want to know what the possibilities are - trust you know what plants to look for - laurel, rhode, yew, azaleas etc will all poison her. Womer? Creosoted fence? Rat wee on hay?
I'd isolate her for sure if only for the sake of your other girls and just make her as comfy and quiet as poss. You can reference back over the TAS threads, there is likely to be info on this in the past violet. All the best, let us know how she goes.