Understand fully suejaw, try having a sister-in-law like that

I'm so close to my brothers, my nieces, nephews and all my other sister-in-laws and my friends. I'm very trustworthy and never
ever gossip about one to the other and have always thought of myself like you as easy to talk too, everyone else just phones for chats or pops in without invitation, but this one sister-in-law will never open up or be friendly like that. Conversation does not flow naturally, I constantly have to think of subjects like yourself, but get nothing back. She is in fact the sister-in-law who lives the closest and we should be close but after all these years she will never open up, she is the same with my mum and everyone else though, but it does make you feel upset when someone is constantly guarded, she shares nothing about her life even silly things like she has ordered a new suite and is having a different hairstyle. :-D
It used to upset me that she stays continually guarded, as I feel we have missed out on a great friendship, but there is nothing you can do, the only person she talks to is my brother. I've just come to accept that is who she is and she will never really be
that friend, or allow me to be a close friend to her, just an acquaintance in a way, you can't force it, and I guess as I did you need to just stop trying, if it isn't there it isn't there.
I think it hits you harder when you are an open chatty person, you can't change her suejaw so just keep her as a friend in the background. :-)
She is the same with my other sister-in-laws too, so I guess it is not just me, but I hear you it is very hard work when people are constantly guarded,