what did the vet say? any progress? has she started eating anything at all?
i was thinking about pika today and thought i'd mention that for some, a dental is quite an uncomfortable procedure. i know it doesn't sound like much, filing teeth, but they have to have their mouth forced open, getting the cheeks out of the way and all and the mouth must feel very different afterwards. from experience, stopping eating is the first thing they do when they're not feeling well (this is teeth, respiratory, gut.. mae even stops eating when she's on heat sometimes!), and given she's not been given any pain relief, it's probably the same as us having a minor procedure and not take anything for it.
as for euthanasia, i would say that the time to think about it is if the dental's been done, she's been on pain relief and hand fed for a few weeks and she's still absolutely refusing to do anything - eating, is lethargic, doesn't want to play, doesn't want anything (they can still bounce back from this state but obviously if it's prolonged, it's probably kinder to let go). also, if she has a dental and is happy to take liquid food, if you have to hand feed her all the time between dentals, it's probably time to let go. but your case is very early days still. let us know how she's doing!