2 things,
1. The dog running into the person during play is very common. The front dog often is looking back at the playing dog in the chase position and they run into people. This is not a Jumping up issue it is a playing dog not paying attention during the excitement of play.
2. Regarding the actual jumping up issue. It appears that you already practiced the standing on a leash when someone approaches so that the dog can not jump up. They are instantly corrected and you still give the Off/Stay Down command to re-inforce.
That said, since it appears you have people/friends that can assist you- try the following without the leash, since that seems to be what you are seeking:
Have the friend approach walking directly in but not talking to you or the dog. When the dog jumps up, they should completely ignore the dog and Stand straight up, looking upwards to make sure that there is no eye contact or attention that the dog is receiving. The instant that the dog stops jumping and her 4 feet and/or butt is on the ground, they then praise the dog and pet her and thus reward her. The dog will soon learn that the only way to get attention is to sit or stand quietly. Again, the reward of attention must be as soon as the proper behavior is displayed, butt or feet on the ground, so that the dog understands what she is being rewarded for doing.
If the dog jumps up while receiving the attention, the person must again immediately stand straight up and ignore the dog until feet/butt are on the ground and the jumping has stopped. Once the dog is down, reward with attention again. Continue this process with many people, over and over again.
Good luck and make sure that you never allow anyone to pet or talk to the dog while the dog is jumping up on them. This only works if everyone interacting with the dog follows the same rules. Your dog wants attention and will soon learn that the only way to get it is by staying calm and under control.