First, I would make sure she is getting no grain, just
medium quality hay to help make sure calf is small.
Does a vet think she has a large enough pelvic opening?
Watch her close and have chains ready.
There are a number of these things each year
and many have positive outcomes.
I think back to my childhood and recall a heifer
that calved like that. She was a fertile girl and
had her third calf before she was three. Every
calf came unassisted. These are marvelous
beasts.