I think this just goes to show that people feel differently about this.
Personally, I feel as Sparkling does. When DC1 was born we had already advised people that we had a "no visitors for 2 weeks" rule. No idea how any of us were going to feel, no idea how feeding was going to go, no idea what state, mentally or physically, I was going to be in. I didn't plan on entertaining anyone just after giving birth. We will have the same rule in place after DC2 is born.
However, what actually happened with DC1 was that things went fairly well and we felt comfortable to visit others and have people visit us before the 2 weeks were up. And because it was sooner than expected people weren't disappointed at having to wait longer before seeing the new baby. We did it on our terms when we were ready and because people were not expecting early visits it wasn't a problem.
IMO nobody has the 'right' to visit someone else's new baby, but new parents or parents of a new baby absolutely have the right to decide who visits and when.
OP I think YABU, sorry, but you do have lots of time to meet and get to know your new niece or nephew. Your sister gets first dibs on the early days and is perfectly within her rights to keep them to herself.
Congratulations on auntie-hood though!