You know what's really messed up?
Elena's greatest trauma in life is losing her parents. So when Vicki dies, she becomes complicit in hiding Vicki's death from both Matt and Jeremy, protecting Stefan, but also protecting Matt and Jeremy from experiencing grief for a loved one. Because it might break them -- like it broke her. She denies them the ability to deal with reality -- by expliciting asking for Jeremy's mind to be compelled, by lying to Matt that she "doesn't know where [Vicki] is." Jeremy earlier in the episode says that the first good times since his and Elena's parents died were with Vicki, which is just like Elena with Stefan -- so Elena knows how terrible the loss of this person will be to Jeremy because she's been fighting to wrench herself free of Stefan who finally made life seem ~normal and liveable again. Like happiness could exist, like she could be okay. Stefan becomes her ~normal even though he's the one who opens the door to her life never being normal again. In one fell swoop, she clings to her redefinition of normal with Stefan, the Other, the most not normal guy she knows, and preserves her definition of true normality within Jeremy by having his "suffering" erased.
God, her costume is poignant. A bloody, tattered nurse who can't heal anyone -- she can only try to stop the blood from gushing forth by hiding the wound. It's a sleight of hand -- and it doesn't help. Avoiding grief doesn't stop grief, pretending you're okay doesn't make you okay, pretending you're not a vampire doesn't make you not a vampire. Elena will cling to her fantasy of normal with Stefan, though she initially tries to reject it by telling him she "can't be with [him]," but people keep dying and "of course it matters" because it's devastating and she can't help but take it all on her shoulders. She becomes the secret-keeper and abuser of trust that she recognized in Stefan -- all for love. By denying Jeremy and Matt knowledge of reality and access to their own grief, by taking it on her own shoulders, Stefan
Elena's this fascinating spectacle of selfish martyrdom. She'll do anything to save other people from pain which consequently privileges her own expression of suffering. "Can you make him forget? [...] It's what I want." Does life get easier for Elena if her brother doesn't have to deal with grief? She can't save herself from grief, she can't imagine ever being "okay" again (though she came close to it in the early days of dating Stefan before that dream was shattered), but if she can cushion Jeremy's fall, does that make it easier for her to go on? Living vicariously through others -- how appropriate for a doppelganger.
Jumping ahead to the end of Season 2, she comforts Jeremy for losing Jenna, but she doesn't acknowledge herself. Because if she's not real, if life doesn't begin to fully matter again, then how can she be hurt? She doesn't want to go through the process of grieving and living and grieving again -- loss is inevitable -- so she directs ~all the grief in her world onto her shoulders, because loss hurts less for her if she has trouble remembering happiness, because no one can carry it the way she can. Obviously, it's also to save others so that happiness can actually exist in the world even if it's not for her, only to discover that as the doppelganger she's "a lightning rod" for pain and suffering brought to those around her. It's a violation of her purpose. She's meant to suffer for them, to protect them all from the grief she knows so intimately, not be the one who brings grief to those she loves. No wonder she gets all suicidal.
Her story follows its natural course; rather than being a bystander to death, she's actually forced to face death, her own death, in order to realize how much she wants to live. But Elena wouldn't be Elena if she wasn't shouldering other people's burdens.