Murdered girlfried... there's a difference. Perhaps I should back up a bit and say that Bonnie's been a bit too petty about the whole Anna thing. After all, it was she who pushed Jeremy away and effectively caused him to feel the need to keep his interactions with Anna secret.
Meanwhile, when Jeremy and Anna first started being able to see each other again, it was simply because they still cared for one another, and neither of them wanted to pursue the other romantically. Had Bonnie not pushed Jeremy away or tried to force Jeremy to choose between her and seeing Anna (who is all alone, mind you), and instead tried to help her 'find peace and move on', things might not have turned out the way they did. Instead, Bonnie was determined to banish Anna into an eternity of isolation purely out of jealousy. That's a bit harsh, I think.