Some children, even though they are adults, feel angry at a parent for dying too soon. Other people feel guilty over unresolved disputes with a parent. Some feel profound sadness. Others feel relieved, then guilty, when a parent dies after an extended illness. Even siblings sometimes experience the loss differently.
Emotions are never good or bad.
You may choose to grieve in a very different way than someone thinks you ought to. Honor the other moms in your life. Perhaps a good friend who's like a mom to you, or a friend of your mother's. Talk with siblings, friends or relatives. The first Mother's Day without your mom, consider calling or visiting other people whose lives she touched.