Don't pull on it. Work on teaching her to follow you when you have the leash in your hand and leaving it loose, but if you get to the end of the leash and she's not following then stop and verbally coax her forward. Give her treats and praise when she takes a step forward. If she doesn't relax after two or three tries, take the leash off and try again tomorrow. Encourage her to watch you, not the leash, and just go where you go...leashes should never be pulled, they're there as a safety measure rather than a guide. It may take her a while to get to where she's consistently walking on a leash, but give her time, she's had a traumatic start to life already, and it sounds like someone decided to try to loose-leash train her by beating on her every time she got it wrong.