Teague does this to Karma. He is never aggressive but thinks he can run over her like she is a greyhound, not a dog half his size! They get along great, but don't play, and Karma has mastered the art of assuring that she doesn't get run over. She will avoid eye contact, keep her head low, and ignore him.
I would just leave things be, as you can't force dogs to play with each other, they will do it on their own when they feel comfortable. If he gets too overbearing or nippy she will probably give him a warning which is perfectly normal. Sounds like they are getting along well, some dogs don't play with each other and some will. Just give it some time! She'll still need to take it easy after the surgery.