Actually I always thought that she just didn't know better. I always suggested that she thought she could save Elena by killing Greta but she wasn't smart enough in that moment to just break her neck, so she tried with biting her which was obviously not a good idea.
I still miss Jenna by the way. I think they could've done great things with her character (but as a human, not another one of these annoying vampires).
Nah, I find it more plausible that her hunger was crazy because she was newly turned, new vampires can't control themselves. On the other hand she actually said "I know what to do" so a part of what you said might be true.
And I agree about her character, she would have fitted in the show as a human.