Foul, though there will be idiots in the stands yelling "but she is fair territory when she touched it." and sometimes those idiots will be standing in the 1st or 3rd base coaches box.
Another one from the "You Should Know Better" department: travelball coach told me that a runner cannot leave a base on a bobbled but ultimately caught flyball until it is secured in the fielder's glove. Runner had left as soon as the ball touched the fielder's glove and he thought we were vulnerable to appeal if the defense had noticed that the runner was already off the bag when it was ultimately caught.