Just wondering, will she eat those things for other people?
One of my partner's sisters (now 10) has always been fussy. She's gotten better as she's gotten older, but even when younger we always had more luck getting her to eat things than her mum did. We never offered her any alternatives, and if she didn't eat a meal then she MIGHT get some carrot or a piece of fruit an hour or two later... otherwise she'd have to wait until the next meal/when she went home.
I don't know whether it was that she KNEW we were serious & wouldn't offer an alternative, that it was a different environment, that at home she might connect trying a new food with having to eat it regularly.. whatever it was though, she would eat/try things she refused to at home, and some of those things she would then eat at home when she decided she liked them.