L.C.
Most car seats that are front/rear facing are 5lbs on up. There shouldn't be a problem with her weight if you have on of these. My sons were both too heavy way too early and we moved them into a front/rear facing car seat and they are just fine. If she's too big for the seat then move her. If she’s not comfortable move her. Do you like being cramped in small seats? If you don't I bet she doesn't. Go head and if you still don't think you should then ask her Doctor.