There is always a possible risk with all pets being fixed - especially spayed females.
The most common, is weight gain. With dogs and cats, it is possible to get lumps, arthritis, and tumors - but this is mostly seen in dogs. In fact, that's how one of my dogs died.
But don't worry, I've never heard 1 report of rabbits getting these problems other than obesity. Neutured males have a very less chance of gaining any type of problem, in which would only be obesity and laziness.
This is what I've witnessed, I've been told, and seen with my own eyes. I have a very fat female cat. My other cat is in fine shape.
But since there are others saying it's fine, there's probably nothing to worry about. If any type of problem occurs from it, it would be weight gain. I really don't understand how it happens. It's a little complex to understand.
Other than my cat, I don't nueture any of my pets. I have 2 male buns,and yes, they can become naughty, but like all animals - discipline is required. My parents failed to discipline our dogs(And their fixed.),one of them notorious for his ignorant behavior, started hurting my other dog in play fights. One day he hurt him really bad till he had a hard time walking - and unfortunately had to get a new home.
If you only own one rabbit - then you really don't need to fix her, though that is your choice.
Don't take my post seriously. I'm just putting in my 2 cents. I just happen to be one of a kind.