As many have said - you need to clearly tell your husband what worries you, what angers you and how you think this should be fixed (approached). But first of all ask him if he really wants to work in the shop. If he doesn't, then you should talk about what he would like to do and how he sees your future together, what compromises each of you can do to support each other.
Also, I know it's hard, but maybe defend your husband in front of her, and say you like it the way he handles things and you trust him. Maybe try to turn every of her complains into a joke. So she would see that she has to talk to him herself, and that you have her son's back :) And tell her if she continues bossing you around you'll not produce her any grandchildren (￢‿￢ ) (≧▽≦). Sorry. I don't really know how to help you with the she-devil (｡•́︿•̀｡). But you should stand up for yourself. If someone is using your kindness to manipulate you, and you know they do, it's your responsibility to defend yourself. Or be used forever (×_×)
P. S.: Visiting washroom seems like a valid reason to leave work to me xD. Also, I personally find smiling shop keepers creepy (≧▽≦). Polite is enough for me.