Perhaps you can tell her you are going out if she wants to come over even if you not intend to. If she insists to come over then let her be, you just have to leave for a stroll, coffee, movie or shopping etc. Whether your hubby wants to go with you or not, let him decide. He may want to spend some time with his mother.
To go over to your in-law's house, you need not have to follow your husband everytime. Just my two cents worth.