Well, I've heard many times now that they often do such things because they get a reaction out of us, so the best way might be to not 'react' in a way that shows her that you 'care' that she does this (eventhough it might drive you nuts inside). It's a mess, definitely, but as my pediatrican says, you have to stop (and explain why) truly dangerous behaviour, ignore annoying behaviour (such as this), and praise positive behaviour. (And yes, it's a lot easier said than done.)  Just clean it up as if nothing interesting happened, and calmly try to continue feeding, or wrap up if she's finished.

We are having pretty good luck with my daughter.  She's 18 months old and has gone through her moments of throwing food down, but mostly she does not.  We tried a few things so I'm not totally sure what worked the best!  For a while I would sit beside her and only give her 3-4 pieces of food.  If she threw one, I would tell her calmly that we don't throw food down.  If she threw another, we'd repeat the message take the tray away for a minute.  It seemed to work sometimes.  Then we thought let's give her another option...so we said if you don't want it, put the food 'here'.  The place we told her to put it was the cupholder of her highchair tray.  To our amusement, she started a habit of picking out the unfamiliar or unliked food and putting it there - not on the floor!   Now that she is big enough, if she does throw pieces down, I get her to help me pick them up afterwards, so at least I avoid some of the bending and crawling around!

We still avoid giving her too many pieces of anything at once as it seems to invite her to play with it rather than eat.  As I say, the odd time she does pitch something over, but mostly not.  We are thrilled with that!