I did that a couple years ago when we were in Africa.
The pool itself doesn't have just a whole lot of flow over it. It's kind of like an infinity pool with just about a half-foot of water going over the rock that separates the pool from the Falls. So to go over, you'd probably have to purposefully slide yourself over.
Even so, there's a reason the camera doesn't show her feet. That's because there are two guides with her, one holding each ankle. And then there's a third guy back there just as an extra hand.
Getting that photo isn't the dangerous part. The dangerous part is getting out to Devil's Pool. That's where you're walking out on very slippery rocks that have about a foot of flow going over them. One misstep there, and you can go for a tumble and be swept just a little bit downstream over the Falls. That's where you really rely on your three guides. They've been doing this since they were kids, and they know exactly where to step (and, more importantly, where not to step). They lead the way. You have one guy holding each hand while you take a step. And then between steps you grab the hand of the next guy. So anytime you're taking a step, you have two guys holding you.
But anyway, you get out there and look down, and the view is amazing. This video doesn't even really do it justice. I went at a somewhat higher flow time (early July), so the flow was such that you couldn't see anywhere close to the bottom. All you see is the mist, which is actually coming back up towards you. It's just staring into a wild maelstrom with a background roar that is almost deafening.