It's interesting how some JW's expect you to just come running back and be so grateful that they threw you a crumb after being so hateful for so long. Anything could have happened to you or your family while she took her time to forgive you or whatever it is she is trying to do. No thanks to her, you have a nice family and you are all safe and sound.
I also find it interesting that your Mom "friended" you a day after you made your post here about having been "thrown away" and also that she did this on New Years Day or Eve which is also the 100 year anniversary of the oh so important 1914 date.
It's a long shot I know but do you suppose she or someone else you know, could be lurking on here and saw your post and figured out who you were ? Or what if, because of the 100 years of waiting, on the part of JW's, she's having second thoughts about their history of failed prophecies and is also rethinking the whole shunning thing?
Either way, I think you have the upper hand in this situation now. I like how you let her know that you weren't even sure if her contacting you was intentional and might even have been done by mistake. If she's ready to start treating you decently, the ball is in her court but it's up to you to take it or leave it. For better or worse, you only get one Mom so who knows it might be worth another shot.....I'm just sayin'.