Well, I don't really agree with most of you.
The pensieve is here to show what happened in someone's life. The pensieve does not take feelings into account, resentment, happiness or anything like that.
It just shows in a neutral way what happene from someone's meory, but I don't think the memory can be altered by feelings in this case.
May be I'm wrong, but I think the penseive is really showing us what really happened, neutrally, despite people's feelings.
and by the way, Snape tells Harry that indeed he's using the penseive to prevent Harry from seing things he doesn't want to reveal.
But as for who the penseive belongs to, I can't say if it's DD's one or another. I don't remember.