Did you and your mother-in-law get along great until you gave birth to your first baby? Does it seem like she won't leave you and your family alone and that she is trying to take over your life? Life transitions can bring on new problems in old (once stable) relationships. How can you help to ease the conflict?
As a new mother, you are at the stage of development in the family life cycle in which it is essential that you and your partner create a boundary around your nuclear family. It is very important that you and your partner align loyalties.
You ARE the wife and mother in this family. It is important that your authority be recognized in the extended family. Instead of feeling trapped, find your voice as a mother. You and your husband set the guidelines in the family. Explain to your mother-in-law that you appreciate her as a grandmother. Ask her how she would like herself referred to. Would she like your child to call her grandma, nana, or some other appropriate endearment?
Let your partner know that you do not expect him to love his mother any less, but that you are now the center of his life and need his support. It is his job in the beginning to talk with his parents about boundaries you two have set. He must show his mother that he supports you in your parental authority and require that you be accepted as his wife and the mother of his child. Not saying anything for fear of his mother's reaction will only worsen the situation and can reinforces her fantasy that you are merely a "third wheel."