While I’m pregnant now, it’s my first so I don’t have personal experience, but I have seen many of my friends deal with this (both with their mothers and MIL), as well as my sister.
Some things I’ve noticed and have thought about for myself:
It seems to work out better when boundaries are set beforehand. If you mainly want help with staying on top of the housework and getting a chance to have a shower, I would say so. I have one friend who found her MIL toweling off her newborn after giving her the first at home bath…no photos…and MIL didn’t ask before doing it. Friend was napping. MIL thought she was helping, but my friend was pretty upset. My friend has not forgotten this.
Your hormones are going to be a mess. You’re going to cry a lot and be exhausted and super sensitive. If you MIL annoys you normally, this may get worse for you. So, I might think of some coping strategies before she gets there. Serious lack of sleep and mental exhaustion can equal massive issues.
You shouldn’t be worried or thinking about entertaining her (or anyone else!). If she is someone who normally expects to be entertained, again, I’d let her know that’s probably not going to happen. If it does, great, but you’ve got other things going on. I know that this has been a problem for some of my friends. You come home with a new baby, haven’t slept for 48 hours, and people arrive wanting snacks and dinner. Figure out that stuff now. Freeze meals or let her know that your DH is cooking. If you have a good relationship with her, you might mention that you would love it if she cooked X dish.
Different parenting styles lead to problems…so, if you’re a person who is of the cry it out variety (even with a newborn) and your MIL wants to comfort Baby, this will lead to problems (saw this with my BIL and my mom). It really doesn’t help if MIL and either you or your DH are of one mind, because that leads to issues with your spouse. Maybe talk about that kind of thing ahead of time.
Accept help when offered if you’re comfortable with it. Now isn’t the time to try to be everything to everyone. I’ve seen this happen with my friends too. Let MIL do laundry if she offers (and hopefully she will!), etc.
Sorry this is long…but clearly I’ve been thinking about this too. 🙂