I'm so glad she is bright
Drinking is really important because it helps process the GA through her system.
Rabbits vary. She may need another dental quickly, she may need one many months down the line, maybe even years. It really can vary depending on the problem. I do think though, that whilst 6 weekly checks are maybe useful, you are the one who needs to be super vigilant because you are the one who will pick up when she next needs one by her behaviour.
With regards to the timeframe, I don't believe that IS normal vets advice. Really, I think it depends on the bunny, how they cope after the GA, how their nature is generally, etc, as to what is and isn't fair. Some bunnies have a GA every 3-4 weeks, some many months apart.
My Sky takes about a week, plus, to recover because he can't cope with being somewhere away from me. If he needed one every 3-4 weeks he would spend most of his life recovering, so I would have to consider if that was fair.
Equally, I have Roger who is petrified of people and handling and if he needed GAs that often, I would have to work out if that was best for him.
On the other hand, I have Wish and Autumn who bounce back very quickly, and Wish is very dental and we would have done every 3 weeks if she had needed it. I've had others who would cope fine with dentals every 3-4 weeks too (although my bank balance would be taking a severe hit :lol
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I think really, while making a decision on what you think is best for her, look at what she is telling you, not at what the vet is telling you (might be helpful to read my 'Please Remember to Advocate for your Bunny' link in my sig- for a couple of reasons). Obviously don't just disregard the vets advice, but put your point across for what YOU think is best for her and make sure the vet hears. If he doesn't, try a different vet