Why is my puppy acting so aggresively with other dogs?

As Walt said, its hard to evaluate without more observation. but in my experience, ur having typical signs of play biting, which is kind of normal for a dog her age, especially if she has been separated from her mom and siblings at a very young age. because mommy dog usually corrects that behavior when they do it to her, and playing with siblings her own age, would mean they are having the same behavior and they are rough play biting with each other, which makes them realize "heyy, thats annoying and it hurts sometimes" and they stop doing it how long have you had her for? and when did these behaviors start? where was she before you got her? how much exercise does she get daily? these are all factors to how you can move forward

Hard to give advice when you cannot actually observe the behavior but I would recommend you contact a local dog trainer for an evaluation and probably a few training sessions.

I would agree with Walt, you should contact a local dog trainer. One that not only does general obedience but one that has worked with aggression. As with any profession, you have some trainers who only know the basics. Where on the other hand you have some trainers who had really studied and have a wider field in knowing more of your specialties such as working with aggressive pets. Just make sure to do your homework. If your Lab is showing signs of early aggression, you want to nip it in the butt now before it really becomes a problem.
Good Luck!