You could get adult sized OK stuff again years ago, I've still got a lovely 50s pump attendant's jacket... If you can be arsed it might be worth searching for them...
I'd recommend a trip to @JD's vintage emporium in Camden and grab a pair of OK or Lee dungarees... Late 70s soulboy classics...
Thanks - she's 5'8" so I'm not sure Osh Kosh will fit.
Afaicr their stuff was for littler kids? (Should have said that she is growing up size!)