Have you tried exercising the dog for a while before formal retrieving training session to burn off some of her energy? This may help calm her down.
You mentioned that after a few retrieves, she will start going early... you need to have control over her to prevent this, be it a check cord or some other method to keep her from "jumping" the command to retrieve. She needs to learn that she can't go until commanded to do so. Along that same line, have you been doing large percentage of denials? If the dog has been trained where every tossed bumper is her's, it could be why she doesn't wait for being told to fetch.
Finally, regarding blind retrives... set the dog up to succeed. This means very short blinds at first and set her up with the wind coming towards her and have some scent on the bumper. This means putting scent on the bumpers you toss for regular retrieves, so that she associates that scent with a bumper. This will help her know that a bumper is there without seeing it when you send her on the short blind retrieve.
Have her under control and if she doesn't go, take the first step with her at heel. towards the bumper and let her discover it is there. When she does find it, even if you walk her to within 2 feet of it, praise and reward her a lot. If things are really difficult for her, you could train short distance blind retrieves using the scented bumper or a favorite
"smelly" treat at a very short distance indoors. You could start this in the house with a hidden treat in a hallway and tell her to "find it/hunt it up". She can only go down the hallway(keep it short by not using the entire hallway length) so that she will succeed. After she has learned this, you can transition to outside training, again, with a light wind blowing the scent of the treat towards her from a very short distance. Finding the treat will instantly reward her for going out for the blind command and since she can already smell it and wants to get it, she will comply with command for blind retreive.
Again, start very short and easy set ups to insure she succeeds then build from there.
Good luck. Go slow, maintain control over her and reward your girl for getting it right.
Michael