@AnneSims34 Did it occur this fast on your other save or did you have to play longer ? If it already occurred after 3 days on your other save, it sounds like it's a problem with the save game.
I think it's probably easiest if you go on playing with your other Sim and make a note on what date she should be aging. Once that day comes around, just manually age her up and then see if she's fixed for the next stage.
There are certain hidden trait that prevent aging properly but if that was the case then the version in your new save would also not be aging.