I posted about this on WWYD before, but I think its more an AIBU 
My DB and SIL have been married a year, they have a young DS and baby DD. I adore my DNephew but haven't really had an opportunity to bond with my DNiece (have only seen her a few times). Over the years I have seen my nephew loads and have helped out when my DB has been so strapped for cash he couldn't afford to by DN new clothes etc.
However my SIL has always been a bit... well, odd. I think she has severe PND and has never let anyone spend time alone with the DNs - by which I mean me and DG's aren't even allowed to take him into a different room in the house where she can't see him, let alone take him to the park or out for the day
Obviously this has been really upsetting for our parents, who are almost at the end of their tether. When my parents visit they aren't even offered the baby to hold after being there for several hours. DB won't confront SIL on these issues and seems to think that they are not too extreme (even though he isn't allowed to be on his own with his children!)
I had my DD 5 months ago, DB and SIL's first niece or nephew. It took DB 6 weeks to visit, and he came on his own. I never got a card from them. Now I understand with his own young family DB couldn't drop everything and come over but he did use to drive almost past our house on the way too and from work. The first time he was supposed to come he actually forgot! He has now seen his niece a few times and has been very loving with her, and he brings over clothes DNiece has grown out of, which is really kind of him. But he has to sneak the clothes out of the house as SIL doesn't want to/doesn't think of passing them over. Not that that's bad on its own, really, its just with everything else that it adds up.
What really makes it bad to me is that DM found out last week that SIL has not asked a single question about DD over the entire 5 months, even when DB has been to see her - basically, she has never mentioned her name or acknowledge that she exists.
I don't drive so it isn't possible for me to get to DB's on my own steam, but I should be heading over there with my parents quite soon. DM is adamant that if SIL doesn't acknowledge my DD or doesn't ask for a quick cuddle (we suspect this might happen as it would mean SIL putting her own DD down for a minute) then she is cutting ties with SIL and will only see DB and the kids on their own. I'm not sure that I blame her.
SIL's birthday is coming up very soon. Normally I would buy a present but I don't even feel like sending her a card or a text - though I know this will be seen as a huge slight. DB had a massive go at our parents for not sending a card when they got engaged (we're not really a card family on those occasions, so I don't know where he got that idea from).
I'm starting to stew over this. I don't mind so much for DD as she has other uncles and aunts on my DP's side who dote on her and plenty of our friends who are 'aunts' and 'uncles'. AIBU unreasonable not to acknowledge her birthday?
(Sorry, this turned out longer than I meant!)