Also, now that it's on my mind, remember how VM had no problem killing James but certainly seemed reluctant to kill Lily? He could not have forseen that Lily's sacrifice would protect HP--DD has said as much a number of times. Well, if she was the person who helped Regulus steal the locket horcrux, I can understand why VM wouldn't be so quick to kill her. If Regulus had been killed by then (and I'm certain he must have been) Lily would then be the only person who knew what became of the locket. VM tried to talk her out of standing in the way, but he eventually decides he has to kill HP and, therefore, he must kill Lily. Why did he decide this was okay to do? Because he didn't realize he was about to be separated from his body.
It's pouring here! We've been having heavy rain every night (except last) for the past three or four days. I bet those d*mned dementors are breeding again.
I imagine that Lilly Evans (Potter) was supposed to be a "reward" for Snape in exchange for giving LV the information about the prophecy.