Is she in labor or just looks like she could pop at any moment....but won't? I am thinking you mean she looks ready, ready, ready to calve but just hasn't yet. My experience with heifers is that this is very common. In our case, we have some heifers we have thought were going to calve for 2 weeks now, but nothing yet. They are springing very heavy, udders look tight and full but they just aren't ready yet. They will be ready when they decide, that is all I can say. Heifers can start to bag up a month before calving so you can't just go on the external signs. Some don't look near ready and calve first, just how it goes.