DH, his parents and his siblings are scattered across the globe. We used to be very very close to his sister. Regular calls, texts, emails and visits.
Since DS was born a year ago she wants nothing to do with us. We used to Skype her monthly and email more regularly than that, and we've heard nothing from her since DS was about 4 months old, aside from the occasional "like" of a picture I post on FB. I email her photos (copying in other family members, friends etc) and ask how she's going. She runs her own business which hasn't been doing so well over the past few years but she used to talk about it with us and we tried our best to support her. I would go in and help her out at work when I visited her.
She and her DP live the fab/hip/cool/edgy life in a trendy city. She's late 30s but has said she's not sure whether/when she will have kids, so I don't think she's jealous of us having DS or anything like that. A couple of her friends have had children recently and she slags them off a bit for moving to the suburbs/not wanting to come out anymore. I'm not a complete new-mum bore I think - I mean I do post photos fairly regularly on FB (2-3 times a month) and email more personal photos round to close family and friends including her. But I'm not one of those forever-updating-about-PFB-types.
When DS was very young we went back home and she came to visit us with her DP, but she spent most of the time working and not wanting to hold DS or do anything with him. She kept calling him "it" instead of his name and it was a bit annoying really. But overall it seemed like a good holiday, when she wasn't working we did get to do stuff together and it was fun. I just don't understand why she's so quiet now? I just can't get through to her. DMIL has said TBH it's just like what DSIL does to her - no replies to emails, calls are very rare (couple of times a year etc).
It makes me sad 
and I have given up emailing her to set up Skype dates because she never gets back to me. She doesn't reply to DH's few emails either - although it's always been me that was the one setting up Skype dates etc. He's annoyed at her but is a bit like "that's just what DSIL is like". I don't only want to talk about DS to her and bore her with kid stuff, I want to hear about her life, what she's doing, her work, all the stuff we used to talk about. I am worried about her because from what I hear through DPILs her biz isn't going well and DH and I would like to just be there for her and listen, even from a distance.
AIBU to not understand this at all???? Or more precisely, is she BU or am I BU and should just expect this as part and parcel of having kids ie people don't feel like they have anything in common with you anymore? I know it's hard when you're separated by distance too, but I keep in touch with friends in other countries quite regularly (monthly/bi-monthly skypes etc) so it's not THAT hard....