Why is Lisanna always a b****?

Most people think NaLu is amazing (I agree) so then they see lissana as a threat so they try making her thêm of a monster that natsu could never love.

Remember she was separated from everyone for two years and was in Edols. Then there was the seven năm gap so she's been through a lot. Natsu made a promise to her that if anything would happen to Lisanna he would save her. But when she "died" he couldn't keep that promise, and Lucy kind of reminds of Lisanna in one of the episodes. But she doesn't know what happened to Lisanna until Levi tells her.