Hi, have you ever read a story linking the Lady Nimue-Vivian and goddess Diana the Huntress. I read somewhere that these 2 women were related by parentage (something like Diana, usually said to be a virgin goddess, being an ancestor to Nimue-Vivian's family) and that, one day, Nimue-Vivian's father received a prophecy by Diana that her daughter would learn magic from a great wizard (aka Merlin) and become the Lady of the Lake, but I don't know if it's in some of the "official" Arthurian texts
Hello! I didn’t know about this connection so I searched online and while britannia.com only makes a (unsourced) connection between Viviane and Diana’s names, I found that there is a plot connection between them in Merlin Vulgata.
Bruce’s arthurian dictionary describes it like this:
The Roman goddess of the hunt. According to the Vulgate Merlin, it was her enchantment, given to Dyonas, that caused Viviane (the Lady of the Lake) to be so alluring to Merlin. […] Diana is mentioned several times in Spenser’s The Faerie Queene. She raised the huntress Belphoebe, who became the paramour of Arthur’s squire, Timias.
Unfortunately I didn’t find anything about the specific plot you mentioned! but maybe someone out there knows more!