Deb framed Hannah, I'm pretty certain of it. In the hospital when Dex comes to see her she wants him to think Hannah has poisoned her. She mentions Hannah visiting her, mentions that she could have broken in, she plants the seed in Dex's mind that Hannah had tried to kill her.
I think there's a reason we didn't actually see Deb crash. She never blacked out, she had 3 times the amount of drugs in her system, but we don't know when she actually drank the water. Were there any witnesses to the accident?
Deb needed to get rid of Hannah without Dexter turning against her.
Hannah definitely knows Dexter gave her up. The only evidence there was against her for Sal Price's murder was the pen. She has to know Dexter has given this to the police.