MIL madness

I'm a first time mom with a super over barring mil. Shes a nice lady and I think her hearts in the right spot but she will literally ask you something and then do whatever she wants anyways. I'm concerned when this baby arrives (which is anytime now) shes going to start showing unannounced and stay for hours at a time and she kind of exhausting to visit with all the time. I want her to have time with her granddaughter but I also want her to respect our decisions (my husband does tell her she needs to chill, I just have a feeling it's all about to go down hill). She literally gives me anxiety and drives me up the wall because if she were anyone else I'd put them in their place......I guess I really just needed a place to vent.