I got the impression that all of the paintings in the house Michonne and Carl found were painted by someone who lived there (there were so many of them, all in the same style) so I assumed the 'mum' or whoever painted it after she killed her family bit before she did herself.
It was very sad - though none of the bodies looked small enough to be the children inhabiting those rooms. And the layout was really odd (I may think about these things too much).
Regarding Rosita and her daisy dukes, even if she wasn't worried about zombie bites, surely wandering round like that in a world without doctors/medicines (amazing magical animal flu healing medicine excepted) is just crazy. A small infected scratch could kill her*
*Though obviously a punctured lung, gunshot wound or amputation would heal in a matter of days 