You know, she will know he is in jail. If it were my child and his or her father were in jail I would be doing some serious checking to see what is going on when my child was there with him. If she is too concerned she could always contact you.
If you feel the child is in a dangerous situation you could always tip off CPS in the future if needed, you can do so anonymously and then leave it alone.
Good Luck in moving on!