I work with our procurement team a lot. One thing I would say is they are often more smartly dressed than others. If you consider how the role works they are often internal client facing [so providing key services to senior people with budget to spend] and also facing out to sales people who are rarely other than the very smart end of casual.
It's best to see how the land lies than end up with a bunch of stuff she won't wear. Or a ton of very dull stuff that isn't her.
I would also recommend smart classic separates rather than a suit. Having a good jacket black or navy is key for trousers and over dresses. Boden do a lovely velvet or velvet cord one every winter for example. Useful to contrast fabrics rather than have a suit that isn't a suit if you know what I mean? It just looks cheap.
Lots of women wear dresses and trainers in the office now especially in summer. All the way to the most senior levels though they might have a smart pair stashed in a drawer for a board meeting. Hardly anyone wears heels unless its boots. Over the knee is a no in any sort of corporate environment.
We are smart casual. I'll usually wear a dress to the office, or trousers jacket and a blouse of some sort. Never jeans because I am not skinny enough to wear them and still look smart. If jeans appear in our office it is more likely on men with a very smart shirt and blazer with proper brogues or grad scheme/interns who are always cut a bit more slack plus they are often in the digital / marketing space which is far more casual culturally even within the same firm.
The advice I have always been given is to dress for the job you want, not the job you have. Senior people will always look more favourably on their replicas even if it's subconscious.
Lastly, good haircut, polished nails not talons, decent accessories will all make her look put together and professional.