Actually, her very existence was a miracle. Her parents were old and barren, but her mother one night had a dream in which she was told she would bear "a beloved child of Christ.". The woman vowed that she would give her daughter over to the Church. Her biographer, Rudolf of Fulda, tells us:
Shortly after the woman had made this vow she conceived and bore a daughter, whom she called Thrutgeba, surnamed Leoba because she was beloved, for this is what Leoba means. And when the child had grown up her mother consecrated her and handed her over to Mother Tetta to be taught the sacred sciences. [Life of Leoba, Abbess of Bischofsheim, by Rudolf of Fulda]Leoba's exemplary behavior made her a natural fit for Boniface's mission to Germany (also, her mother and Boniface were cousins). A dream of Leoba's, that she would have great influence and accomplish many things, prompted her to join the mission.
Boniface established Leoba as the abbess of a convent in Tauberbischofsheim. (Tauberbischofsheim is the capital of the Main-Tauber district; its first mention in history is in St. Leoba's biography.) He gave her jurisdiction over all the nuns of the mission, and when he later left for Frisia, he gave her his cowl to indicate that she was his steward while he was gone. (He never returned, being martyred in Frisia.)
Later, she was given an estate by Charlemagne near Mainz, where she retired with several nuns. After she died, on 28 September 782, miracles were attributed to her intercession. When her relics were translated 50 years later as a result of her canonization, and placed behind the altar of a church in Fulda, Rudolf was given the task of recording her life. Rudolf says he witnessed some of her miracles himself: a man from Spain had terrible twitching in his limbs that was cured after lying prostrate before Boniface's shrine. Her explained that he had a vision of a woman who presented him to Boniface for his blessing, after which he woke up and had no more twitching. (Why this is a miracle of the woman and not of Boniface, I cannot say.) In another case, however, a man who had been bound by iron rings had them come off while praying before Leoba's shrine.