Would her contacting my sister and sister in law be consider a change in behavior? I don't know, seems pretty random to me.
No, I would not consider it a change of behavior.
Continue to hold out. A change of behavior would be when she decides she's ready to commit to doing whatever is necessary to save the M. In the meantime, she wants to act like she's single.
Let her come to you. Do not make it too easy, and don't take her back too quickly. If you do, you will go through this again. Do you know what terms of agreement you would need to try again?
A lot of WW's will temp check, just to see if the H is still emotionally invested. If she sees that he is, her interest immediately leaves. So be aware of any sudden contacts where she's all emotional and needing you.
Her contact with the SIL, and just the fact you heard about it..........sounds a little like it could have been her just checking things out to see what you've been doing and if her "position" in your life could be threatened. Know what I mean? The best thing (for your M) is for her to hear that you ate happy, and getting out there in your new found freedom.
Most LBH'S are scared to death for his WW to think he isn't holding on for dear life that she'll return to him. Actually, if she is wayward.......that is not the message she needs to get. She needs to be concerned she is setting him free, which means he can replace her with someone else. A better woman, A woman he deserves. A woman who would respect him and treat him well, and give him all the love he didn't get in his R with her.
As long as you sit around pining over her, then she's fine with it. For some reason, a WW wants control over him......even if she doesn't want to be his W. The jealousy factor is still there. Her thought process is all messed up. It makes no sense the LBH. Selfishness and jealousy usually spurs her behavior.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
