This is very good for you and I think that should be the attitude of all daughter-in-laws! If the mother-in-laws don't respect themselves, we don't need to respect them either! I think your 99 wanted to test your bottom line to see if she can manipulate and bullying you.....so wicked and ridiculous!
I think she's a bit crazy and has a low self-esteem since you come from such a nice family and well educated.....
For this:
"Your house is my house, I can come to eat and sleep whenever I want, I don't need to ask you." "Whatever belongs to my son belongs to me."
I don't see how she can say that, that is your house not her son's! If I were you, I would have tell her directly that, 'well, if you son pay me all the money I have put down for this house at once, you dream will come true with no doubt!' ......sorry for being mean......