What I would first of all suggest is to purchase a gentle leader.
http://www.doglikenature.com/store/v...16001&googlead
it is a harness type thing that goes over the dogs nose and the leash hooks under the chin, they cannot pull at all because you are directing the head. It is not a muzzle at all and they can still do all their normal activities, it just puts you back in control. I would try that while you are working on training again. This way you can practice comes with a leash on her and don't have to worry about being pulled over. Remember to never yet at her if she comes to you (it's hard when you are frustrated) but come should never mean punishment. Come should always equal praise and cookies (while you are relearning it). Also while you are retraining her I would never let her outside without a leash on. When we learned come in puppy class we were told to never say come unless we were willing to back it up. Meaning if you say come and the dog does not come then you must go get them and bring them to you. But since you can't do this (due to the running) don't say come at all, just put her on a leash to do her business and that's it. Does she like to play ball? Will she bring it back to you? If so that is a perfect training opptunity, when she is on her way back to you with the ball say "come" and when she gets to you have a party and give a treat. Oh, one more thing I remembered, when she does get to the point that you can let her off leash in the yard and she comes, don't always make come mean time to go inside. In other words you are out in the yard with her she is playing you say come, she comes over to you, you have a party and then she is allowed to go and play some more. Part of the issues you might be having is come means play time outside is over. So by calling her to you and just because and then letting her go play again, you are telling her come doesn't always mean playtime is over.
I hope this helps.
Gina