Welcome here! She is a cutie!
Buns do well with alfalfa in their diets until about 6-7 months, then you can begin to switch over to timothy completely. It isn’t necessary to do both alfalfa pellets and hay, so if you wanted to you could start switching her to timothy pellets within the next couple months and continue some alfalfa hay until 7 months. It’s up to you how you want to proceed. I adopted my mini rex at approximately 4 months and fed her exclusively timothy pellets and hay with a few handfuls of alfalfa here and there and she did great on it.
Rex breeds are more prone to being overweight and developing sore hocks, so you want her to always be more on the lean side. Your vet will be able to evaluate her and tell you how much she should weigh for her breed, age, and build.
Females are usually not spayed before 6 months. Some vets will do it sooner. Those nasty teenager behaviors may kick in anytime between 3 and 8 months, or you may never experience any behavioral problems. It depends on your individual bunny. My mini rex was an angel until about 5.5 months and she turned into a little terror between 6 months and when she was spayed at 7 months. Almost immediately, the behavioral issues were reduced.