Hello Lin! I'm Chels. I play Negan and Carl here, and am thinking of bringing in a third who's allegiance is undecided atm. I'm not sure I could offer much out of Negan until their paths cross in Alexandria, but Carl is in need of friends. Especially ones who know what they're doing in this new world.
I for one wouldn't mind her joining their group prior to finding Alexandria. However, they weren't really in the trusting new people head space at the time of the barn setting with what just happened at Terminus, so I'm not sure how well that would have gone down.
Perhaps she could have been freed from Terminus and joined them then? Otherwise I would suggest Arron/Eric finding her on her own.