Well, I'm the same height although my problem is being short waisted. In that case she probably needs to wear separates but these ranges will fit on the shoulders which is one of the problems with 'normal' sizing. There is also Top Shop petite range and some of the items may fit, they are very small, but they do tend to be young styles. If there is a problem with waist and hips not fitting look for either a dropped waist or an empire line dress. I got a lovely Fenn Wright Manson dress last autumn with a vee neck, and an under the bust seaming which is lovely and would avoid that problem.
Or of course, you could get out the old sewing machine...