A.C.
If she is in a forward facing seat behind the driver, the mirror on the passenger's visor works great. Just unlock it from the little clip next to the rearview mirror, and then push it in toward the windshield. This is how I've always viewed my nephews when I drove them.
(If she is behind the passenger side, you can do this with the mirror on the drivers side visor.)
For a rear facing infant, you will need another mirror attached to the backseat for this to work. Unfortunately, I haven't found one that sticks properly on my car.