pildough,
All of us who had our baby falling off know how it feels like exactly ie. guilty guilty guilty. Don't let it eat you up. My baby fell from the sofa when she just reached 5 month, on her face, her soft, button nose to be exact, on the cold hard homogeneous tiled floor. I don't know how she did it, but it sure sucked - for me.
Felt guilty for a few days after that, but it made me more careful and watchful.
Do away with the condemnation. We'll get better at being mothers.
As for your mil, ask her to go fly kite.