eek! My advise would be 24hr turnout, with ablib hay or hayledge so there is constantly food available to eat, out with other horses preferably youngstock if you can so she/he can play with others for social interaction and prevent boredom (basically give her something else to think about!). I've heard on here it can be linked to gastric ulcers and if the weaning was very abrupt this could have aggravated the condition bringing out the windsucking, get this checked out, there are supplements available for horses prone to gatric ulcers aswell. Basically give the foal lots of stuff to do and hopefully it's young enough to possibly forget, I've never had dealings with a foal that did it, only an adult, by then the habit was so ingrained no matter what you did she always wind sucked.
Definitely eeek!! Very unusual in a foal - where did it come from?, how old?, and how has it been kept?
I've only heard of one foal that windsucked before - a neighbor bred it and it windsucked the day it was born, literally!, had heaps of vets to look at it and they had never seen anything do it that young! Turned out the stallion she used had thrown loads of foals that were the same - how weird is that!? It did for the rest of its life too, he was very hard to keep weight on, kept getting choke, and he stressed very easily - fantastic showjumper apparently despite that and did very well!!
I'd ditto what competitiondiva said - 24/7 turnout, I wouldn't stable it for the next few years at least to see if you can get him to grow out of it, turn out with other horses, preferably a mixed herd of calm oldies and a few youngsters, with add lib hay/haylage.
I'd also get the vet out to scope him and see if he does have an ulcer and go from there.
On the gastric ulcers front, my mate used Naf Magnesium and mint supplement and it worked brilliantly. Not sure re it's use for younstock though so you would have to speak to one of their nutrition people.
Great advice above - don't try and physically prevent it windsucking, distraction and a happy horsey environment is definitely the best treatment!