Trauma after school

Hi parents, have anyone experienced this & know what to do? My 21MO daughter recently started school in a playgroup which is for 2hours per day. Since day 1 we put her for 2hours straight alone because she seemed fine ( i should have sat in with her which i didnt ) . On day 2 & 3 she began crying badly because i heard kids were snatching her toys & pushing her. Then the episodes began... she started waking up around 2am & insist on leaving the room & she would be fine when she goes to the living room but i will have to follow, when i refuse she will go on screaming & crying for 2-3hours till she slept because shes too tired . Then we began to realise it was for all her afternoon naps & bedtime sleep.. she will not want to be inside confined in the room & repeating her crying episodes ... it is so bad that she gets so tired she fell asleep on the floor. We do not know what to do anymore...