I think the budget of around 6k will be the tail end of the first generation E87's or early E81s
Petrol as opposed to diesel? the mpg of the diesels seems great
Ah missed the budget, to be brutally honest I think they're all pretty rotten outside of the 123d(which has its own issues) and 125/130i - none of which would be suitable here.
That said, there will be no arguing with a female who has decided what she wants - probably as well to buy as nice a 116/118i as you can find. Skip the diesels, not worth the risk.