Okay i thought maybe you were giving them water to play in which isn't a good idea since they can chill so easily at the age they are, but putting her into some nice warm water for some exercise wouldn't hurt at all and can help and all the ducklings would love it. Just make sure to pat them dry and put them into a nice warm place to finish drying. Giving her some swim time can help build muscles and also take pressure off her leg.