I work in an office of gorgeously dressed young women! In fact I like to think I was one of them before I got pregnant 
Are the offices she's interviewing at very corporate ie suits for all? If not, I would suggest the following:
Blazers - at least one black but don't all have to be, prints and bright colours (if acceptable in her offices) will keep the look fresh and not age her. I would suggest river island and miss selfridge for these, topshop also do very well tailored ones.
Dresses - can be from anywhere as long as they're smart, for her age I would suggest river island, topshop, Zara, oasis
Blouse/shirt style tops - shops as above
Slim fit black trousers - as above
Shoes - when I wear heels to work I tend to wear medium heel to work to be honest as I couldn't go all day in the very high ones I would wear on a night out/to a wedding etc, Dorothy Perkins and new look do some which really aren't yucky as long as you get the right style - eg leopard print to brighten up a plain dress and pointy ones. There's some on the DP website at the minute which have a skinny metallic heel. Also ankle boots might be appropriate in the A/W, fringed ones are still very in and again they give a plainer dress a fresh look.
Add accessories to keep outfits looking fun and varied. These I would always get somewhere cheap like primark as they're no worse quality than what's three times the price in topshop etc.
I miss my pre-pregnancy clothes! Good luck to her x