Here is the solution. Hire a sitter and don’t “use” your MIL. If you have complaints about her then you are not building a good relationship with her and are only using her for your convenience when you have grievances against her. If you have grievances against her you should NOT be using her.
Work on your relationship and try to understand where she is coming from. If she is a worrier and you are a calmer person then she is not the type of person that should be watching your kids if you want to go out and relax. If she comes over and asks to take your kids out, that is a different story. My mom A”H, used to ask me when I am coming home and that made me nervous and made me feel rushed when I went out. If I agree to babysit for my kids I never call them to come home and if they call I tell them to take their time and enjoy their night out.
If your MIL worries when your kids are sick, don’t tell her when your kids are sick. If she comes over when your kids are sick, reassure her before she asks that your child has….and that you already took him to the doctor who is not concerned. Then involve her by asking if your husband ever had…. and what she used to do for it. Then you can let her know how things are done differently. In that way you are including her and informing her about today’s methods.
When I am with my grandchildren I have to use today’s methods and not what I did when my children were babies. I know NOT to put babies on their stomachs or even on their sides like when my first grandchild was born. I have to keep up with the changes. So my daughter and DIL’s talk and discuss with me. I don’t complain but I do have questions at times. When I asked why medicine wasn’t given at a time when my grandchild was coughing I was told that medicine is no longer given at such a young age. So that was something new for me. When my kids were that age, they were given medicine.