I can totally see this happening! Only... In my mind Petunia would resort to violence and Sirius, being the good boy he is, would mobilize her with some spell and leave her for Lily to take care when she got there :D

Also, I've read your Beautiful The Way You Are on ff.net, I just wanted to say it's really beautiful :) It's a very difficult theme, but you brought it up in a way that made everything make sense. I'm not very good at explaining things, so I guess it's better I stop before I start rambling, hah :)