It's an adult dog's job to teach puppies their manners. If she is just holding them down, and they don't appear especially distressed, I would not worry about it. Do they continue to play with her after she does this? This would demonstrate that they are okay with her behavior.
I would intervene if the dog being held down starts to sound distressed, or if multiple dogs gang up on each other. As a general rule, you can interrupt doggy playtime every few minutes, just to keep things from getting out of hand, and reminding them that ultimately, YOU are the biggest dog in the house.
