I think both of you have extreme situations - to have siblings babies born on the day or right after you miscarried.
My niece was born 3 months after my m/c but for me, she was always going to have her baby before me so I coped with that and was happy for for my brother and his partner - and was happy to cuddle my beautiful niece. I'm not sure I could have coped the same way if my m/c had been right at the time of her birth though.

oreobaby and I hope you are okay with meeting your niece, and celena - while i'm sorry your SIL wasn't more sensitive, I'm glad that you were able to feel joy in holding your niece.