please help me with my preschooler!!!

My daughter has been going to the same preschool for two years. Her aunt is even a teacher there. But every single time I drop her off, she clings to me, won't talk when anyone talks to her. She just shoves her fingers in her mouth and stands behind me. I wonder if there's anything I can do to chang this behavior! I can't understand why she's not comfortable! But everytime I pick her up after school, she's playing and having fun, so its just when she first gets there.

I explained to Tanner, who recently turned 4, that sometimes mommy doesn't want to go to work either. But I go to work so we can watch cartoons and go to fun stuff and have toys. And if mommy doesn't go to work we don't get to do fun stuff. And if tanner doesn't go to school mommy doesn't get to work