My DH/me and his sister fell out badly about 9 months ago. It was very acrimonious and we have not spoken with her at all since.
We have a dd together and my dd from my first marriage who DH is step father to. His sister always treated my dd as family, bought birthday presents etc.
My DH's nephew (sister's son) had a birthday about 4 months ago. We bought a card and sent money (he's 19 and at university). Didn't even think about it really. We always do send him money/cards for birthday/christmas and its his mother we're not speaking to not him.
Since then both my dd and our dd have had birthdays. In our dd's case, her first birthday. And no present/card was received.
AIBU to be upset about this? Its us she's fallen out with not the dc so why punish them?
She's still their aunt after all.