My favorite Dog is the Cavalier King Charles Spaniel - and I have two of them. The best dogs I've ever had - very smart- easy to train- very loving dogs - couldn't ask for better dogs- they love you and want love in return. They are pretty easy dogs- I happen to have 2 tri-c0lor Cavalier's and they are superb.
And if you are a single male - they are a babe magnet - women love them -
Well first she is 4 1/2 months old - and is recovering from a broken leg - why not go easy on her for a few more months. Perhaps it is painful for her- did you think of that? Dogs remember things that hurt them - so go easy - have shorter walks and think of your dog more - of what you can do for her to get over this.