My pup is the same, despite my taking her to flyball several times a week, puppy class and also hanging out with her at schutzhund training. Part of the problem is in flyball and schutzhund, they spend the majority of their time in crates, and not actually meeting other dogs. Then in puppy class, they do have a few minutes to play at liberty, but most of the time is spent working on training.
She's in her first day of doggy daycare today. I'm anxious to see if I have a tired/happy puppy tonight, but I think if you need socialization, that is a good way to go, if they can be introduced in smaller groups.
I'd look into finding a good daycare place and maybe let her go one day a week, or even for part of a day. That is nothing but playtime with other dogs, all day, so she'll for sure get lots of exposure to other pups and be tired and happy when she gets home.
Good luck, my pup is 4 months old this coming Saturday, so i know how much work it is! Also, if you don't have kids, make sure you spend lots of time at parks & splash pads. My pup was fine until a toddler scared her, now she's a bit timid around kids, so we're working really hard at that now.
ETA: be very careful at leash free parks, because a lot of people with aggressive dogs think they will do the same as you, and socialize them that way. You don't want her to have a bad experience with a problem dog. Leash free parks are not the place for socializing aggressive dogs, but a lot of people think this is the best way to do it. I think a daycare is a better bet, where it's supervised and the dogs are all temperament screened and UTD on vaccines.