I personally would keep sending her only to help keep the routine going...

Maybe speak to a staff member there about how the best way to say goodbye is, sounds silly but sometimes a quick kiss and 'mummy will be back for you soon' might be the best thing for her (not sure what you do already)?

I read somewhere playing 'hide and seek' may help in some cases as it reassures the child that mummy will be coming back, IYKWIM?