She’s not oblivious. She made her expectations extremely clear to Tom- to her their relationship was casual. His mistake was thinking she either wasn’t serious or would change her mind. He did not tell her he felt that way, so from her perspective she thought he was fine with their relationship as it was. That is not her fault and she did end their relationship when he made it clear he had different expectations.

She was characterized as being outgoing and friendly. Those traits don’t equal “leading someone on”. She was intended to be a deconstruction of the “manic pixie dream girl” trope.