well, I am not the best person to answer this...

But you know, I don't know why a decorative slide wouldn't be professional. That sounds like a good option.
I bet your flamenco with a flower style is very lovely, although I understand your hesitation to wear it. I probably wouldn't, either. It's too bad, because a hair flower obviously isn't going to affect your work skills, but people can be silly in their judgements sometimes.
If you are really worried, you could sacrifice fashion for a day and wear that bun that you don't like...it might not look so horrible to the folks at the fair as it does to you! But then maybe you would feel pressure to keep wearing it at work and that would be bad.
I hope you have good luck at the fair and find work that you like where you can wear your hair however you want (and that has insurance benefits!)

Good luck again!
winterwren