Kate, has DH tried giving her the EBM when you're not there? Often they won't take it while mumma is around, but will when they're not. My DD wouldn't take EBM from a bottle or dippy cup, but did take it from an adult glass while I wasn't home and she was hungry for milk, so it might be worth giving yourself a couple of hours of mummy time soon covering the time when you would normally expect her to feed.
As far as the BLS goes, I think it's wise not to rely on it - every child develops at her own rate and while there's every chance she will have made steps forward by then it's not a definite and she will still need her milk anyway. FWIW, I spoon-fed DD yoghurt, porridge etc (foods you would normally eat on a spoon) initially, until she had the coordination to get the spoon into her mouth herself.
I think you should talk to the supervisor, I don't think it's unreasonable to ask for a bit of extra time to feed, especially as it's only one day, and you could also offer to take a little less pay to cover that time. I reckon it's better to know where you stand up front.
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