Business casual for a 16 year old

[Inniu]

DD needs business causal clothes for a summer programme in the US.

It will be hot outside and air conditioned cold inside.
The guidelines are smart trousers with dress shirts/ polo shirts/ knits. Or knee length dress/ skirt. Nothing sleeveless, no visible back.

DD is a curvy 8.

Any suggestions?
Everything I have come up with is to old.

www.matalan.co.uk/product/detail/s2680679_c101/slim-fit-formal-shirt-black

Uniqlo has great rayon shirts that drip dry and don't need ironing if you hang them on a hanger when wet. They're fab for work and they dry overnight. (And not too expensive, and travel well. A couple of those would be good.)