My DD is same age dress size and build and had a similar interview recently.
She wore a black shift dress with short sleeves and a matching blazer, with black opaque tights and black low heeled shoes ( she can’t even wear mid heels ).
It wasn’t expensive, just from H and M, as she won’t need to wear clothes like that in the job. Next have similar inexpensive office wear.
Simple jewellery , hair and make up, as others have said. Most girls of that age are used to wearing A LOT of make up and very short ( bum skimming ) skirts, but this doesn’t look appropriate in a professional job. It’s not the time to “ show your personality “ and “ be yourself” unless the job is in fashion , the arts etc.
There were lots of other applicants at DDs interview and all the other girls ( bar one ) were wearing similar or trousers / skiirt and blouse.
The odd one out was wearing an outfit that was more appropriate to a wedding , with very short skirt, high heels, bare legs ( yes in January ) and a lot of jewellery.
Boys were all wearing suits/ jacket and trousers expect one boy in a leather jacket and jumper.
DD originally wanted to dress much more casually but ( for once) heeded my advice and was glad she did.