Sometimes the buns dont know what theyre missing out on till theyve tried it...i swapped one of my older ones onto excel but like yours, she didnt eat it, so i cut down on the quantity of food for a few days so she was a bit hungry (she still ate her veg and hay though) as she LOVED her food, and she eventually tried it, then that was the first thing she ate everyday as i swapped her over.
Unfortunately my older older bun just plain refused to eat it, iv never been able to put her on it!
Dont worry too much, its only the first day, your bun might just be wary of it as its new, my two younger ones were the same with new veg, didnt want to try it but after a few days they had a nibble and havent looked back since. J
Just be patient, try leaving that amount for a few days, if no luck try cutting down the total amount of food whilst leaving the same proportion, and maybe your bun will be hungry enough to eat it. If its there overnight she might nibble on it if your lucky...Good luck!