Im sorry that i cant answer this question.
I have never had a bunny fixed. Im thinking of getting my boy fixed, what happened when you got your bunn neutered?

Yes you still should spay your female rabbits no matter if they have bred or not. The chance of uterine cancer is close to 90% above 5 years of age, and can also happen in younger does. So for health reasons spaying is recommended.

For girl and boy rabbits, fixing also helps with behavioral and hormonal problems! I’m sorry you had a bad experience neutering before On the other hand, neuters and spays have very high success rates if done by a rabbit savvy vet. Generally the benefits of fixing outweigh the risks of surgery!

http://wabbitwiki.com/wiki/Uterine_cancer

This is an informative article with a lot of good links in the references to scientific study. The general medical consensus is that rabbits are more prone to uterine cancer as they age. Age is the dominant factor in all the studies. Differs,t studies have different percentages, so whether it is 80 or 90 or 70, depends on the study in question. And those numbers are for rabbits 5-6 years of age. Younger rabbits have lower percentages. While I have read and been unable to find again – an article discussing uterine cancer in bred does, 99.9% of research does not cover that question as a hypothesis statement, but does say that age alone, regardless of breeding history, is the dominant factor.
It is a tough choice to make for some people, and no one can tell you what to do. Read through these articles in the reference section.
While there is risk in any surgery, the risk of a spay-gone-wrong is far lower than the alternative.