I don’t think you’re a terrible person, or a monster. This behaviour is likely to make most people claustrophobic, and it is strange even if she wasn’t being overbearing with it. Hard to see how you could have a healthy relationship with each other at present, especially when she reacts so strongly to you communicating your own expectations/needs. I’m not sure what to suggest you do, I just really wanted to reassure you that you’re not going crazy or overreacting, because most adults don’t behave like your sister.
There’s likely a reason behind it, whether it gets addressed in her therapy or not. You don’t mention how your parents treated her, though? You don’t have to, of course, I’m just wondering how her upbringing might have contributed to this.