I agree that she probably was short bred when you bought her. All according to what type of preg checking was done, a vet can miss them through palpation when less than 35 days, and sometimes even further... 45 days. If done with ultrasound, a good vet can pick it up at 30 days.... but everyone is fallible on occasion. So, a late January or early Feb breeding could mean a calf in later Oct/Nov.
Jerseys bag up differently... some way ahead and some within a few days. So, as
@Dsth mentioned... do you have any idea when she previously calved? You can take the date you bought her, and back up 60 days as anything over 60 days can obviously be felt if palpated for pregnancy....
Unless you have a vet to recheck her, you are going to be guessing. If you breed your own cows AI, then anyone that is skilled in AI can palpate her and tell if she has a calf in her..... I can tell them after about 4 months.... and have picked up some that are shorter.... but after 5 months, the fetus is plenty big enough to feel it.
Check her udder to make sure she is not developing a case of mastitis. Sometimes they will get a flare up if there is alot of fly problems and they can carry it. I have seen virgin heifers come down with mastitis months before calving. I bought one off a dairy at about 7 months bred that had developed mastitis in one quarter as a dry bred heifer... the quarter was no good from the start but she milked out of 3 and the next year only out of 2... but I got a nice heifer out of her that I still have.