I would give her a second chance. If she gets back up. 80 lbs is an ideal weight, but a lot also depends on the shape of the calf. A big head, square shoulders, or a blocky calf can cause problems even with smaller birthweights.
As for her not wanting to have anything to do with the calf, that happens a lot when you have to assist a heifer. Usually we will leave them alone for a couple hours and the heifer will have changed her mind. However, in this case, I wouldn't worry about it too much, she had a pretty traumatic time of it and it may take some work on your part to get her to accept the calf. For now I would worry about getting colostrum in the calf, and getting the cow up. Once you get her up the calf will win her over, after all she will be pretty unsteady, and if the calf is agressive at all it will win (As long as she doesn't fall on it). Good luck, and keep an eye on her next year. If she gives you problems then, then cull her.