I just wanted to thank everyone here because I finally got up enough courage to talk to my MIL myself. No more waiting for dh to understand my need for boundaries with his mother.
So, last night, I told MIL that we needed to talk and I told her that for me as a person, to be happy in my life, there are certain things that are important and that I need. And, one of those things was time with the family I created with dh. That, because I work WOHM FT, I have very little time to reconnect with my ds and dh each day and so the time I have is very important to me.
I explained that unannounced visits make that time difficult to come by and when she drops by, there are times that it's NOT a good time, for whatever reason.
I told her I want her to feel welcome in my home, but that I need time with my family too. I stressed the importance of her relationship with ds and that I hoped to develop a better relationship with her over time.
Then, I asked for 2 things:
1. for her to always call before coming by
2. for her to understand that when she calls, there may be times that it's a BAD time
She tried really hard to understand and at the end, she said she understands my need to spend time with my family, but she said she was lonely (she lost her mother in December.)
I told her my goal was not to alienate her or contribute to her loneliness, but that I needed certain things in my life to be happy and time with my family is at the top of that list.
I left it at that and she said she'd do her best. So, now I just have to be strong enough to make her hold to her word