Possible premature calving question

Ive got a first time bred heifer due in mid march, but some clear fluid is coming out of her vulva, which is a sign she will calve soon right? Does this mean she will calve immaturely

Not necessarily. A little clear mucous or discharge isn't uncommon. It's just her system beginning to lubricate and get ready, even if it's still a few weeks away. My experience is that calves usually won't come earlier than about 10 days before the due date, but I've had them as much as 2-3 weeks and do just fine. We had one last year that was over a month early (twins) and we were able to save one of them. She was touch and go for a few days, but she's doing great now!

When she actually gets ready to deliver, she'll lose her mucous plug which is the plug in the cervix that keeps any contamination from entering the uterus where the calf is. That'll happen a few days before delivery, and you may or may not notice it or be able to tell it from some heavy discharge. As long as it's clear discharge, I wouldn't worry about her. Discolored, white or yellow might be a sign of infection, and I would consult a vet.