Did your daughter seem depressed after her abortion? Do you think she may have regretted it? A very common symptom of post abortion stress syndrome (p.A.S.S) is the obsession with becomming pregnant again, to do several things, but above all many women describe the need to "replace" the baby that they lost. This may be why your daughter didn't take the proper measures to ensure that she didn't become pregnant again. She will likely, however, feel uncomfortable discussing this with you, and deny it. Celebrate this pregnancy, (if my theory is correct and she regretted the first abortion, it dosen't seem likely that she will want another).
And as far as preventing her from getting preg again, i'm sure a screaming infant will be incentive to take a depo shot
best of luck "grandma-to-be"
~.Laura