I think the notion of a work smartphone is dead in the water now. Any smartphone by definition must send e-mail, hook up with MS Exchange, even have apps to have remote IP PBX extensions. It's kind of like saying is there a good PC to do word processing or spreadsheets, well any can, as MS Office or Open Office can run on any platform.
I don't think OS matters in your friend's case either. It's down to personal preference. She could get a high-end Android like a Galaxy SII or mid to low range like a Galaxy Ace. It wouldn't really matter, since they both send e-mail, connect to Exchange, can be a remote extension by default.