At times the duchess looks rather wobbly on her high heels. She probably wears them to make up for some of the height difference but I would be fine with her wearing lower heels and walking and standing a little more steady and not hurting her feet as much.
Agreed that she often looks a bit wobbly but I really think it's more to do with the fit of her shoes than with any trouble walking in high heels. I think she'd do just fine if her shoes actually fit properly but I can't think of a single pair of shoes that I've seen her wear that don't appear to be at least a half size, if not a full size, too big. I'm going to hazard a guess that many of her shoes were purchased during her previous career and as such she employed the trick that many people use in purchasing them a bit big so they'd be more comfortable during long hours on one's feet. However, when a big part of her job now is to be able to comfortably walk during engagements, walkabouts, tours, services, etc. she really probably should invest in some new shoes that actually fit and will allow her to walk without the wobble.