Dobrev's character Elena was turned into a vampire at the end of the show's third season, after sacrificing her own life to save Matt (Zach Roerig).
Speaking to TVLine, Dobrev suggested that Elena will not have an easy time adjusting to her new life.
"I think she's gonna freak out. I think Elena is not going to be happy about it," she teased.
"Because she didn't even know. She kind of accepted death, and told Stefan to save Matt, not herself."
Asked whether she thought Elena had made the right decision in choosing Stefan (Paul Wesley) over Damon (Ian Somerhalder), Dobrev mused: "I don't know if there is a right or wrong choice.
"I think she definitely tested the waters and made an educated decision, and I respect the decision. But anything can change at any moment."
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Dobrev has said previously that portraying two vampires on the show - Elena's new incarnation, and her undead doppleganger Katherine - will be a challenge, and that she is looking forward to finding out what kind of vampire Elena becomes.
The Vampire Diaries will return to Thursdays at 8/7c on The CW in October. In the UK, the series airs on ITV2.