Hi J.!
First off, congrats on baby girl number 2. I know you guys must be super excited but a little overwhelmed with everything at the sametime.
I know what you mean about a lot of changes. Two days before my wedding I found out I was prego, and 4 days after my wedding, we were moving across the country because the hubby is in the Army and we were being stationed somewhere else. My mom wasn't happy about it and the stress ultimately led to me losing our little one.
So where's the advice, right? Sorry, getting there. You can handle the situation a number of ways. You can either have a sit down (face to face) with your Mother-in-law and just tell her how you feel. I would recommend doing this as early as possible. She'll respect you for handling things this way and it'll probably make you and her feel a lot more comfortable about the stay.
Or, you can talk to your father-in-law. Not necessarily complaining about anything but just letting him know how you feel and asking him for any advice he may have. You know, without a doubt, he will go back and talk to your mother-in-law so be careful with your words here.
And lastly, you can just deal with it.
I would recommend talking to her though. From what you've said about her, she doesn't seem terrible. It just seems like your relationship is on the fence. Bottom line, you will have just given birth, you are the mother and the wife to her son. You are in charge of what happens and you shouldn't make yourself miserable to make someone else happy.
I wish you the best of luck with the c-section and if you ever want to talk or vent :-) feel free to email me. ____@____.com
S.