Dogs don't mount just for reproduction. They also mount to show dominance as well. So she is likely to be a dominant dog. If she is pinning them to the floor, then it is not just a passive dominance either but aggressive in nature.
In most cases, if a dog submits to a dominant dog, then the dominant dog may not pin them to the ground. In cases like this, she needs to learn that you will not tolerate aggressive dominant behavior from her. In addition, she needs to see you as the boss. So to help stop this behavior, you need to start her on obedience training. A training class would be great, but I'd start at home first so you have better control of her when you get into a class and the instructor can help you finish training when there is distractions present.
The following site is helpful for teaching you how to train your dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
This obedience training will help her see you as the boss and as the boss, you determine what other dogs are allowed to do, not her. You will need to discourage that behavior. So keep a leash attached to her and if she attempts to mount another dog, give a short tug and a firm "NO" as a reprimand. It is not going to be a quick fix, but going to take a lot of work. This may help her stop mounting other dogs she may still be aggressive toward other dogs if they are dominant as well.
You will need to learn dog body language to stop her from displaying any aggressive behavior before it has a chance to start. You can learn about dog body language on the following pages.
Bat Training may also be helpful depending on the degree of aggression she shows towards other dogs. If fights are occurring, definitely try the techniques on the following site to help with the issue.
I hope this information is helpful to you and you are satisfied with my response. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have .