Remember about Caroline's sudden remark, no one wants to talk about it at all. They were too shocked, even to believe too hard. Especially Jeremy, the man who knows best how Caroline doesn't want to be tagged shortly.
But because the Vampires knew about him having Mate, the girl suddenly wanted to be tagged. Was the girl sure of her decision, but he felt unsure and Frey also asked for time to think because this was too sudden.
Yes, it was indeed Frey who asked to tag each other in the first place, but the girl refused and suddenly she just wanted to. Of course, Frey was shocked and thought it was all a dream just like Jeremy. But Caroline's suddenly acting like Omega made them think badly.
Chances are, the Heat Caroline's time will come back.
"How many months has it been since the first Heat?" Jeremy asked making Frey remember her Heat Caroline days vividly.