Yeah that's interesting, I don't remember anyone ever using her full name in the show. I could be wrong though. At first I was thinking maybe the E was a storytelling tool / clue, as in Naido is O Diane without the E on the end.

Yes they do. Episode 16 for example. 

'These are the Mitchum brothers Janey E. They're friends of Dougie.'

I wonder whether he told Diane about being the husband of her half sister once Diane came back?  'Oh by the way whilst you were Naido I was your half-sister's husband for awhile and we slept together.'  Diane replies 'That's okay shall we drop into this motel here and re-consummate our relationship?'

when Diane mentions relation to Janey-E to Cole....she says "we're estranged"...the follows quickly with "I hate her".....I love the way she says "I hate her"....there is some guilt & relief in that line that stuck with me....I totally bought that she was her "sister" and wasn't misleading the Blue Rose Task Force...little did we know that lil' owl was not what she seemed