Is she your first bully breed?
Seeing as this breed usually matures into dog aggression I wouldn't add another until she is 2 or older and I would go for an adult male. Still no guarentee they will get along forever or not fight but helps your chances. This breed really doesn't need doggy friends though as they were created to fight other dogs and you won't be able to leave them unsupervised ever. If you get another dog it should be for you, we added a year old male to our 3 year old female and while they tolerate each other they don't really play or seek out the other.