Tina is her twin brother's keep, but she's not particularly good at it. Bobby is addicted to Jet but instead of trying to get him off the stuff, she supplies him with a little hit occasionally. She says that it makes him happy, and that makes her happy. She's tried to get him off Jet before, but is convinced it's no use; she shut him in his room for a week to try to get him to quit cold turkey, but he was back using not two days later.
At the end of the quest Dependency a glitch stops you from being able to move Tina DeLuca to a settlement.
Fix: In the quest you need to chose all negative speech options when confronting Bobby. He will attack you – you should kill him. After this you should be able to move Tina to a settlement (if you successfully passed the Charismaspeech option).