I agree that cow would be calling if calf was gone. Of course, she would only call for about 12 hours. If pasture is rough or brushy she may have hidden the calf.
Didn't someone post on here about twin heifer calves where one disappeared? Turned out the cow was hiding them and only one at a time would follow her up. Both were black so couldn't tell apart from a distance. Finally found second calf hiding place after a couple weeks. Cows can be sneaky. If she is not over bagged then she is nursing something. I would give first time heifer a second chance before dumping her since she took care of the calf for the first 2 weeks that you could see her. Unless she has other problems.