First of all, it is not necessary to treat in-law as his personal enemy. Understand that in her eyes you are a man, which is now responsible for almost the most expensive man in her life - her son. If before she saw to it that it is time to eat, sleep, go to work, now it will do you. Sounds strange, but in fact your husband, serious man in the prime of life, for it is still a child.
It is only natural that it tends to give his "baby" in the caring hands. So the best way to reach out to her mother in law - does not adapt to it, and to show that you really love her fiance, and in the future - husband. How to do it? Here there are no tips because true love has always seen.
There is one more point about the adjustment to. Should be the boundary between respect for the other person's habits and attempt to imitate it. Do not play and do not pretend: you are, what you are, you will not alter or modify. A simple example will illustrate the situation. Suppose your mother-in-vegetarian. Not necessarily to say that you do not put meat, do not wear fur and actively attend the meetings of the defenders of wildlife. Simply to respect her choice, not start talking about the meat diet, do not look for anything forbidden, while visiting it, and cook meat and other "wrong" in terms of vegetarian dishes, inviting guests in-law.
Moreover, if invited a few people, you can cook a meat dish, but it served to separate a portion of one side dish or a specially prepared salad. It only shows your respect for her. In any situation, a stay, because in-law to become a member of your family is not for one day, but for life: the deception will inevitably be revealed, and regain the trust would be extremely difficult.
To find an approach to in-law, do not need to invent any special way. It is likely that you do not immediately find a common language - but not in a hurry to explain it to her prejudice. You belong to different generations, and you need time to get used to each other, to find a way. Be patient, and you will probably be able to do it, because at least one thing in common you have: you like the same type of men!