Definitely find out whats going on at school, working closely with the guidance counselor, teacher, and/or school psychologist. Make sure there are no bullying issues, or teacher issues. I remember being in elementary school, and some of my teachers gave me some real anxiety, just because of their mannerisms or teaching styles.
It could be something like school refusal, or it can be separation anxiety. In either of those cases, its really important for you to be positive and reasurring, never minimize her fears, whatever they may be, but stand your ground and dont feed into it. If she's fine once she gets into school, then deal with the morning fears by a quick positive separation on your part. Quick hug and kiss goodbye, "I'll see you after school", and GO! Let her guidance counselor guide her to class, or to her office if she initially needs some time in the AM to ease into the day, but whatever you do, dont let her hang on to you and prolong the situation, will only make things worse. And ask that her teacher and guidance counselor monitor her throughout the day...let her have a "safe" place in the school if she becomes really anxious or upset, but do not let her go home early. Contact me if you have questions.