The Vita Sadalbergae, has not always been considered a Merovingian saint’s Life. Bruno Krusch, the text’s editor for MGH, argued that it was dependent upon a later version of Jonas’s Vita Columbani and indebted to Carolingian attitudes towards the monastic life. In 2003, however, Hans Hummer published a convincing defence of the text’s Merovingian origin, in which he demonstrated that the style of the Latin, the hagiographical motifs, the sources used by the author, and the text’s social environment all pointed towards composition late in the seventh century. The reference in the text to the ‘recent’ civil war between Dagobert II of Austrasia (r, 676-9) and Theuderic III of Neustria (r. 673 and 675-91) is probably then a good and genuine indication of a date of composition in the 680s, and likely before the Battle of Tertry in 687.
The story of Sadalberga herself is intriguing. She was the daughter of Gundoin, a powerful duke. She married twice, the first marriage lasting only a few months, and the second – to Count Blandinus – producing five children. When the couple separated to pursue contemplative lives, Sadalberga founded the convent of St John’s in Laon. In one memorable miracle story, she obtained some lettuce by whispering at a gardener at the far side of the garden.
Latin: ed. B. Krusch & W. Levison, MGH SRM, 5 (Hanover, 1910), pp. 49-66 [link]
Translation: Jo Ann MacNamara, Sainted Women of the Dark Ages (Durham, NC, 1992) [link only partial]
Listed in Krusch & Levison, p. 45, but none earlier than the twelfth century.