She’s obviously an entitled little madam, OP.
The only appropriate way to have a baby is to keep it an absolute secret from everyone except your partner and, maybe, your parents. After all, you can’t possibly appreciate how unimaginably boring your baby is to everyone except you and your husband - you are the only people who will find the fact of your pregnancy remotely newsworthy. Even mentioning your pregnancy to another person shows that you consider yourself to be the first woman ever to have a baby, and you must be accordingly pilloried.
Any indication that you are pregnant is also, obviously, a massive hint to everyone you know that you expect them to find your lifestyle choices through presents, and therefore is entitled and grabby. I won’t even go into baby showers, which are the equivalent of walking into your friends houses and holding a gun to their head while you demand that they throw cash at you.
Once the baby is born, you must spend a month in total seclusion with no visitors of any kind. Anyone expressing a desire to visit the baby is clearly trying to undermine your role as a mother, and should be avoided. This is time for you and your ‘little family’, and as you know, when you have a baby you immediately stop being related to your parents and siblings.
Once you are accepting visitors it’s obviously fine for your mother to move in, but your MIL is to be limited to bi-monthly visits of 16 minutes each.
It sounds like your niece has disregarded every single Rule of Acceptable Childbearing, and must therefore be condemned.