Ask the teacher to keep an eye out for anything that might set her off, maybe she's having trouble when she's playing with the other kids, maybe she doesn't want to go to school but when it's over, she doesn't want to leave.
The only other advice I could give is to speak to her pediatrician. Her doctor could certainly tell her mother if there is a medical/emotional reason for her crying.
Sorry, she get very sentimental. When we take her to school she starts crying, the teacher says during the day she must cry about 3 to 4 times a day, She comes out of school at 3 if my sister get there at 3:10 she's crying. It's too much.
Can you be specific about what you mean by "the crying is constant"? At school, does she cry twice a day? 5 times a day?
I know you don't literally mean the crying is continuous, because she wouldn't be in the classroom and wouldn't be able to complete work and listen to instruction if she were actually crying constantly.
Do certain things set her off?