Hi, yes that is very frustrating but if she's deliberately putting up barriers or doing things to spite you because she doesn't want you to think you have gotten her convinced, then as cruel as this sounds, it's her problem. She is very lucky she has a brother like you and lucky she has been told of what might be causing her problems, many have no idea.

To me, she doesn't have much excuse. I get frustrating BS like this from members of my family also and I swear I feel like tearing my hair out. You warn them and inform them and it's like they go out of their way NOT to do what you've said or to do it to spite you. Unless of course someone else suggests it that is outside of the family, then they seem to take more notice.

I would not honestly waste your breath because you end up making yourself ill over trying to help them when they are unreceptive and deliberately difficult.