Two possibilities come to mind. One or more of the calves is sucking her. Secondly, heifers sometime develop a hormone secreting tumor of the ovary or cystic ovaries. A simple rectal exam of the ovaries is called for at this time.
I have an angus heifer we brought in off pasture to start to feed up for show. Another calf must have started to suck her on pasture as she started to bag up once we brought her in. She has been dried off long enough now that the bag has shrunk up for the most part. Does anyone have the secret formula to get the teats and bag to shrink right up enough that she won't get noticed while judging?