Your child will become very distressed if she thinks that the people dearest in the world to her, her mother and father, no longer love each other and that there is a danger that they may separate or leave her.
Children are extremely sensitive to atmospheres within the home, so if you and your partner are going through a bed time, behave caringly and affectionately in front of your child and show that you have concern of each other.
Witnessing an argument is one of the most harmful experiences you can inflict on your child, so that thought should act as a deterrent.
On the other hand, I don’t believe in a united front between parents on every question. Your child should understand that it’s all right for Mom and Dad to have different opinions, as long as they are expressed without acrimony.
Children have to get used to conflict because they are going to meet it very quickly when they leave home. The best place for them to become familiar with it is in the security of their own home.
Most children will blame themselves for any conflict between their parents and will go to great lengths to make you friend again. Reassure your child that she is not to blame for any anger you feel toward your partner, and that you love her regardless.