This is a difficult question, and there is controversy regarding this reported special blessing. This issue stems from a reported apparition that Marija received while in the United States in 1989.
I might catch some flack for this statement, but the group responsible for reporting this message has been known to sensationalize information. There is no official acknowlegement by the parish of Medjugorje that this message is correct, and actually their stance is that it is incorrect.
We do know that Our Lady offers a special motherly blessing to anyone present for an apparition. The difficulty starts when people claim that this blessing can be passed on by them to other people. The concern is mainly from a theological standpoint that lay people should not be going around blessing other people. As a compromise I would suggest that anyone convinced that Our Lady gave this special blessing and wants it to be passed on do it in the following way: "I ask Our Lady to send you her special blessing in Medjugorje" rather than saying "I bless or I give you Our Lady's special blessing from Medjugorje".