Caroline was surprised, the girl got up to stare in horror at the Mate who looked so serious. Did she hear wrong? Not! She heard it clearly that his Mate asked him to do the marking.
If that happened then they wouldn't have to feel the pain of not seeing each other, but she wouldn't be able to stay away from that Alpha. And Caroline doesn't want to be tied down right now, she doesn't want to be an Omega who just goes along with that Alpha.
Even though part of him is Alpha, but still there is nothing that says that she can be free after being tagged by that man. If she wasn't free, then what about the Vampire? She had to make peace in this world.
Peaceful life for the Vampire and Werewolf, without any war at all. But now that wouldn't be possible if she were tied to that man, and Caroline had rejected him.