Bonnie first died in season 4 when she brought Jeremy back to life. She returned to the land of the living in season 5 but only by becoming the anchor to the Other Side. Her second death took place later that same season when she and Damon became trapped in a '90s-era prison world after the Other Side crumbled.

Does Bonnie die in Season 8?

In the end, Kelly reveals that Katherine's plan was to distract them with the housefire while a now resurrected Vicki Donovan has returned and begins ringing the Maxwell bell to bring hellfire to Mystic Falls; as the bell rings, Bonnie falls to the ground, nose bleeding, and presumably dying.

Why does Elena kill Bonnie?

Bonnie searches for a way to return Elena back to her human state before her transition is complete. She attempts a spell to kill herself so that she can bring Elena back with her, but Grams' spirit arrives and doesn't allow Bonnie to dip into such dark magic. They later head to college with Damon and attend a party.