Talk:Friends/@comment-96.39.252.24-20120426145957/@comment-80.202.171.75-20120426165948

It's explained in this article ;)

NOTE: If after the 24-hour period the gems have not replenished (the gift option is greyed out), try restarting the DragonVale application. To do this, simply click the home button twice on the iOS device to show the running applications. Then, hold down on the DragonVale icon until it starts to wiggle and has a red minus sign on it and press to close the application. Finish by reopening DragonVale from the main application page.