Everyone, even the most notorious serial killer of kittens, has a mother. Some mothers bake apple pies, some program apple computers, but mothers they are. Some live next door, some live on the next continent. Some are cuddly, some are prickly. Some are people anyone would want for their best friend, some make Machiavelli look like a Boy Scout. They certainly come in all shapes, sizes and colours. But regardless, mothers play a role in all of our lives.
Take a minute to take a look at your main character and then squint to see if you can see the imprint of his/her mother. Perhaps it's in their attitudes, or their fondness for chocolate cake. Perhaps it's how they have guilt if they leave their bed unmade or abandon dirty dishes in the sink. It may make them wary of close relationships. It may make them avoid people of a certain physical type - or it may attract them to a type.
The absence of a mother is going to leave a mark too. These characters, although usually highly independent, have a tendency to not want others to get too close. Many will deal with feelings of abandonment or inadequacy.
You didn't grow up in a vacuum. Neither did your main character. Squint. Trust me, she's there.