Why do my baby's eyes wander?

Normal early on. It is quite normal for a newborn's eyes to wander. If the eyes do not move well together by about 6-8 weeks of life she needs to be evaluated.
Could be strabismus. In the first couple of months, it is possible for your baby's eyes to cross due to immaturity of the nervous system. It takes a couple of months for both eyes to work well together. After about 3 months, your baby should not routinely be crossing his eyes. If so, a "lazy eye" could be a condition called "strabismus" that can be caused by weak eye muscles or other vision problems.