I'd probably cut down on sending so much milk until she either takes it or you are sure it's not worth sending it. Perhaps send 2x 50ml serves so they have something to offer and if she takes it then send more the next day. But I'd move to relying on food & water for her day. She'll be fine and you can feed her before and after.

I'd also talk to them about how they are preparing it and send a printed sheet with instructions for heating EBM. I've never come across a child care facility that has done it correctly so they may be ruining the milk and altering it's taste.