If she stops after you leave, then i wouldnt worry at all. Many kids simply have a hard time making the adjustment from leaving mom to getting invloved at preschool. If your child continues to cry after u leave throughout the day, then i would be more concerned. Perhaps you could spend a few days in the preschool helping her become more comfortable. From the way you discussed the teacher, i asume she is doing what she can to help your child.
Some children are more insecure about preschool then others.
She may need help to develop the skills necessary to make some friends.