G.B.
In my many many many many years of experience in child care the parent who brings their child into the classroom, hands them off, then just walks out tends to have a child who will adjust quicker to change and be able to get through this stage quicker.
99% of the hundreds if not in the thousands of kids I have had I can only remember 2-3 that didn't stop crying by the time mom or dad got to the car. Those few kids usually did stop crying within a little while. One of them cried all day for several days but once she realized her crying was NOT going to change the situation she stopped.
As long as you talk about it, discuss it with her, tell her it needs to stop, mention it at all you are giving her attention for crying.
She is going to continue to cry as long as she gets any affirmation that her crying is effecting anyone.
So stop, stop acknowledging she is sad, stop telling her you feel bad about her crying by your actions. Just make her walk in, give her a hug, then turn and walk away. Do not look back, don't stop in the hallway, don't do anything but walk to your car and leave. She may be able to see the car from her room and she'll see if you sit in the car and break down. By teaching her how to do this you are teaching her a life skill.