Angelina
Right,but it could help her to remind her promise,and help her to not break it.Each one have to decide if her promise of chastity includes masturbation or not(even if masturbating,but not having sex,is more abstinence,).
Renita But not enforceable. Unlike wedding ring where you will have trouble with your spouse.
Sure,if she want to wear such ring,she should be convinced to never break her promise,even if there is not much consequences.
She could too discuss it with her parents or her boyfriend/girlfriend and decide she would have to wear a chastity belt if she breaks her promise,even while having the ring on(even if it would be a bit extreme).