She doesn't have much of a charactor really, she's just Draco's mother. The only thing we really know about her is that she has love and concern for Draco.
Reminding me of my favorite line from Goblet of Fire:
'Oh, how easy it'd be to push malfoy off a cliff and make it look like an accident, Pity his mother likes him"
I'll be interested to see who they choose to portray her, if she happens to feature in any of the films (if they continue to make them). I had read somewhere they were considering Liz Hurley to play Bella so if that happens they would have to find someone with even the slightest resemblence as they're meant to be sisters.