Have had the same problem, had been out of work for a while, and when going back to the workplace, didn't have anything suitable! Work clothes are really expensive.
If you can stretch, a couple of pieces will definitely smarten up what she has now, until she has some spare money to buy some more stuff.
I'd say eBay is a great place to look, especially for vintage designer pieces, since they're well made and classic. Also try really cheap high street stores such as H&M for a classic white shirt, a black waist belt, a tailored skirt that she can mix and match with clothes she's got. If all else, stretch to a pair of work shoes and a work bag.
If she can sew or know anyone else who can alter things, tailor trousers she owns, or trim an occasion dress she no longer wears shorter to wear for work. I'm a great believer in adapting clothes to make them work for different occasions. She'll definitely have something that she probably doesn't wear as much, but can make it work.
Hope this helps!