ANYONE can be 'nice'... but that does not mean it is real. People can fake that... WHEN they want something from you. ie: your SIL is getting PERSONAL information out of you.
1) she is manipulative and sounds, VERY highly manipulative and highly seasoned at being... very manipulative.
2) she gossips about you
3) you cannot trust her
4) your inner 'radar' about her, does not trust her. So don't.
5) She may belong to a "cult." And thus, maybe they are told to do things like that....
6) You do NOT know... HOW she is going to 'use' the information she gets from you.... right?
7)You DO NOT HAVE TO, tell her personal/private information. EVEN if she is family. If she asks you questions, just answer with the default answer of "that is private information" or "that is personal. I do not have to tell you...."
Just because she is "family"... does not mean you have to trust her or tell her things or anything else that she is trying to get out of you.
YOU decide what to tell her.
YOU are the protector of your own privacy and personal information.
YOU are the one, to display BOUNDARIES to her. And be firm.
Also, you do not trust her. You get bad vibes from her. She has caused many problems for you before.
So... be WISE. Not the opposite.
The ONLY way, you can stop being a victim of her games and of her mental manipulation...is:
1) to NOT play her games.
2) not let her get away with it.
She cannot manipulate you nor get information out of you/your family/your kids... unless you play her game and let her.
No one can manipulate another... by themselves.