At first, she used to call and ask how I was doing…
then I started hearing things back that I had only told her.
Before you can move on, you will need to stop looking at your former sister-in-law’s blog. It can be facilitated by a therapist, however, and I think in the case you are describing it might be a very good think for you to visit with a therapist a few times.
I know you feel compelled to continue to look at the stuff she is writing, but continuing to view that stuff is making you crazy, and so you have to stop in order to protect yourself. You don’t seem to have people in your life who can validate and support you (you don’t describe such people anyway).
I don’t think your brother’s argument that “he brought her into your lives so he can take her out” has much merit.