Such a sweetie; reminds me of my Alli, my second golden, who would take all sorts of abuse from puppies--she'd look like she would come close to nailing them, and then just roll her eyes to the skies. One of my friends brought her puppy over, who promptly took every toy in my house, made a big pile of it, and claimed it as hers--and my two older dogs just sat there with hang dog looks on their faces.
Is there an obedience class that you can take Miss Happy to? Although it doesn't sound much like play time, obedience classes are great ways to meet other people and dogs--and their are brief breaks during class where the dogs can play. People sometimes meet before class or after class and have the dogs play too, and arrange "play dates" on occasion.
The boxer pup is going thru typical puppy stage right now--and probably needs a better outlet too; although the boxer pup is a neighbor, and is close by, I would look for other friends--more in your dog's age group; it will also help with Miss Happy's submission. She'll never be an alpha, but there's nothing wrong with that.