J.G.
Delete your facebook account. Facebook makes SOO MUCH drama now-adays! (I don't have an account with them nor myspace nor twitter nor any of that mumbo-jumbo).
Next holiday, give her a framed picture of your son and say "I noticed that you had a picture of all the other kiddos but not Joey. So here you go Aunt W!" with a big grin on your face. Maybe let your son give her the gift and he can write that in a note.
W needs to get over herself if indeed she is being selective. But if she doesn't, then I wouldn't worry. Y'all are 20 years apart, so if you haven't had a bonding moment yet, it may not happen or not happen for a while. Not growing up as kids together, there may always be that separation between y'all. Sorry.