I think your mother-in-law 好慘, but i am not sure, and since she's your husband's mother, it is necessary to do that. Your husband will be happy about that even he might not like his mother so much. Well, I am sure she will like you more and you guys can be closer since no one cares about her, and if you are the only one, she will be nice to you so why be scared of her. Especially you have her grandson, that will help your relationship with her too.
I am scared of my 99 but I will try to say jokes and ask her about things, pretend I know nothing, and praise her because she knows more, so I keep asking questions and talk about her son, but of course I don't want to see her a lot.