Lo not eating at playgroup.

My child is 20 months and have been in the same school since infant . She always having poor appetite . But after she got promoted to toddler playgroup , she isn't eating at all for the whole 12 hours . Breastfeed latch on. So I will bring packet fresh milk and she drink alil . But now she refuse at all . I understand toddler's timetable is quite rushing and there is a change of teacher . What can I do to encourage and make her eat in school ? :( I'm Working and can't possibly take care of her myself