Well, that happens, giving birth and refusing to accept offspring, happens rarely but also happens with horses and you are right, is very frightening to watch them attack their newborn.
I would first assume that was a first calf heifer, so she didn’t know what to do, really.
If so, you can tie her and hold the calf there to nurse, they generally do ok nursing twice a day, not as bad as a foal, that has to nurse every hour or two.
Most heifers do give up and learn to let the calf nurse, if the calf is ok.
If the calf was injured and doesn’t act right or has trouble nursing for any one reason, is harder to get her to accept it, calf needs to be aggressive at trying to nurse even if it gets bumped off.
Many prefer just to raise the calf on a bottle, both humans and calf can get injured by an uncooperative cow/heifer.
If all is well and she accepts calf, all should be fine in a few days.
I was surprised that the cow had a halter, ours are range beef cows and definitely not gentle or halter broke, even the pet ones rarely are.
It is hard to get a rope or halter on one to tie her to help a newborn nurse.
No telling what the whole situation was, details make a difference in what to do there.
Glad that everyone seems to be ok, even if the newborn may need to be raised on a bottle, all seems ok with it and the rejecting mother.