I've been told I'm "not allowed" to call in when I've tried to due to weather/vehicle concerns and issues (they sent a cab for me), and been guilted in to coming in when I've been fairly sick, but I think if I have said flat out "I'm sick, I can't
come in" they would have let me call out (with a doctor's note brought in the next day I worked, of course).
I'm sure they get taken advantage of by people calling out when they're not really sick and I know it sucks to scramble for staffing at the last minute and that's why they're so hard on people calling in, but if someone is really, really sick, they need to be able to stay home, and not feel guilty about it.
I'm sorry for your co-worker. I hope she doesn't get treated too poorly over this or lose her job. Definitely look into your facility's policies on call outs and disciplinary action. I'd think a resonable number of absences in a 6 month or year period with a doctor's notes shouldn't be punishable...