With rabbits, you really do have to go based on feel rather than breed. Breeds can vary, even within the breed. A dwarf lop might have a weight range of 4-6 pounds (just a guess), 4 pounds could be ideal for one rabbit and 6 could be quite fat. The rabbit could be within the breed limit, but still not be a healthy weight.
You need to get a good feel of her. You should be able to feel the ribs and spine, but they should not be prominent. A layer of fat is not good either. Rabbits don't carry weight on their skeleton like a dog might, so feeling boney isn't necessarily bad as long as it isn't too much. They should not be too squishy either and that tends to be fat. It is fairly easy to distinguish fat from muscle when you feel them.
If she is going to be spayed soon, that means a vet visit. You can ask the vet if she feels a good weight.
