Hi there, welcome.
Nope, 3 shouldn’t be too old. I think most vets don’t want to spay over the age of 6, so I think even if you don’t have the exact age she should be in the safe zone. They can do pre-surgery blood work to check a few things that can affect their reaction to the anesthesia. That might be a good idea since you don’t know her age or history.
You can ask your vet how many spays they do and what their success rate is. It’s important to have a rabbit savvy vet, so if they seem unsure about it I would look for a different vet.
Funny side note… my girl Bertha was found abandoned in an empty house. Her rescuers took her in to get her spayed, and the vet estimated her to be about 3. When they shaved her to prep her for the surgery, they found she already had a humane society tattoo, so had already been spayed! But there were no records of her at any local shelters. Weird, huh?
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.