User blog comment:Chawk1993/Vivian or Vivienne/@comment-5036924-20120102115209

Both spellings are accepted variants of the name 'Vivienne', although I think I've read that Vivian was initially the male version of the name - not that that's likely to make a comeback any time soon. In older Arthurian works the spelling is very changeable (Viviane, Vivien, Vivienne etc). I would however be more inclined to say Morgana's mother takes the Vivienne spelling, partly as you say to distinguish from Lady Vivian and partly because it, along with Vivien, is (or at least was) the more common female version, I believe.

I imagine it's a slight discrepancy with the subtitling that doesn't warrant a change in spelling on the wiki.