Ask her if the problem developed gradually or rather quickly or suddenly. Getting some accurate history on the problem could go a long way towards solving it.
Could be anything from worn out joints, bushings or other components to a wheel weight that's come off or a tire casing that's coming apart (look for any large "bubbles" in the sidewall or unusual tread wear patterns).
Check all the lug nuts and make sure they're all tight.
Check for badly worn wheel bearings.
Look for accumulated wear in the various suspension components.
If you have a way to get both the front wheels off the ground, grab them at 12 and 6 and then at 9 and 3 o'clock and just move them back and forth to see what kind of play you find, and where. Get the wheels abut 2-3 in. off the ground so you can get a crowbar under it and lift. If the wheel moves up and down, but one or both of the suspension arms don't, that could be part of the problem.
Let us know what you find. Might be useful sometime on one of our cars if it ends up being something rather generic.