Scorpio, on another thread half of mumsnet said that kids should have 'full' names, and the otehr half said they should have 'short# names.
Ella is Danni-Ella, she gets called Ella, even she hates danni-ella, so what was the point of it being on her birth certificate???
Bobby is bobby, I dont like robert, or bert, or rob, or robbie, just bobby, and as it was my dad's nickname I chose it, and called him Bobby, no-one calls him anything else, ELla however gets pissed off being called 'Danni' by people she doesnt know properly.
SO, IMO, call her millie if you want her to eb called millie!