I can say that this is a pretty vague question. You are to give your elders in general respect and that includes mother in laws. Respect is also earned and therefore if you are in a tight spot with a mother in law that isn’t being respectful speak to your husband about it. My rule of thumb is to let the blood child handle it first. When my husband and I was getting married we had issues however we never allowed any one set of family members to disrespect anyone of us. If there was ever an issue the blood child handled it. However the flip is to understand that your husband isn’t going to be able to get his mother to do as he says. She is grown and set in her ways. He is responsible for speaking up not causing her to change her behavior. Once your husband has tried and his mother is still the same way don’t make your husband pay for her bad behavior.
Now that’s in the world where all things are pretty civil. I think when things become to the point where adults can not like each other and stay in their sand castles, than you need to make a plan that works for all. In our case my husband only required that I give my mother in law respect. I didn’t have to do any extras as far as going out to eat, and shopping at the mall if I didn’t want to. He never wanted to force my hand into a relationship. No one should feel forced. If you being the wife can’t be civil than be cordial and move on. If you feel that your husband isn’t handling the situation the way you want than only handle the situations as they come. This means you will have to attempt to allow each situation to be single situations instead of allowing it to build. If you can’t do that only go around when you are with your husband, speak and move on. There’s no written law that says you and your mother in law have to be best friends.
If there are children involved than make sure you give his mother the same fortitude you would give your mother. Keep her involved with her grandchildren and interact with her where they are concerned. It’s a lot easier to deal with your mother in law with the kids than it is sometimes without. If it is to the point where all hell has broken loose and you refuse to be in the same room I think that is a case by case situation. Most mother in law relationships are strained to begin with. Not to say all are, I know of plenty who have the ideal mother in laws that are a direct extension of their own mothers. That can happen when two mature adults are involved as well as have their egos checked and care about someone other themselves. However for the rest of the population I always say treat your mother in law how you would want to be treated down the line and how you would want your husband to treat your mother. That doesn’t mean that it will be a bowl of cherries all the time but keep that in mind because no matter who you are you reap what you sow. So be careful of the things that are said in anger. Be willing to apologize and be the bigger person as much as possible. If you have to say something directly to your mother in law, keep your words on task to the issue at hand, speak up for yourself but don’t be disrespectful, and be consistent. If its totally gutter bad to the point where you can’t and refuse to be in the same room with your mother in law, than so be it but make an attempt to make it better. Sometimes being quiet is a good thing.
The one thing that is always wrong to do with anyone not just a mother in law is to name call. Put yourself in your husband’s shoes if you heard him call your mother names how would you feel? So again feelings are going to get hurt ANY time you interact with other humans. What not okay is to hit below the belt. Even if your husband is soft spoken he won’t forget what you said about his mom and vice versa if he did it to yours. So name calling, hitting below the belt, etc. is wrong don’t let it come from you. There are things we will say that can’t ever be taken back and keep that in mind. If you mother in law does the same for you, retreat. Sometimes some space or not coming around to clear your mind is healthy and no one can tell you that you need to interact. Sometimes we all need some time alone to come back and be better versions of ourselves.