Your child's hand preference is mainly based on her unique nervous system and genetics. By the time she is 2 or 3 years old, she will start showing a clear preference for one hand or the other. Be it pointing to pictures in books, building a tower using 2 blocks, scribbling with a crayon, putting hat on her head, feeding using a spoon or holding a cup, one hand will be dominant and consistently used.
What you need to know
The dominant hand is stronger and has more dexterity, so it's the one she will use more. The most important thing to remember during this time is to never change your child's hand preference. This can hamper her learning and progress due to frustration resulting from forcing her to use the nondominant hand.