Assuming she has no twins or triplets, you could get 16 babies if you were right on top of things and she becomes pregnant immediately upon turning 18 (49 is the oldest she can become pregnant). She nurses for 2 years, then once she drops the baby can immediately become pregnant again. So, it would go like this:

Babies at age-
18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48

Tess