I can tell you what they WON'T call her...I think they will want to use an original name while still being historical...And they won't want a double up, I think Mary will want her precious daughter to be one a kind...
It will NOT be:
Alexandra - the Countess and a nephew called Alexander Stephens (Jane's son)
Kate/Catherine - niece Kate Stephens (Jane's daughter)
Ingrid - Norwegian princess, but it will be a definite middle name, just not the first name
Sophie or Louise - Countess of Wessex and her daughter
Beatrice or Beatrix - it's possible but Princess Beatrice of York and Queen Beatrix might rule it out
Eugenie - Princess Eugenie or York
Victoria or Madeleine - the Swedes
Margrethe - definitely a middle name and if it does happen to be used as a first name they will use a nickname with an "Aussie" feel perhaps, Princess Meg, Princess Maggie or even Princess Greta...
Elizabeth - still undecided on this one, it sounds very English to me, I know Queen Elizabeth and the baby share a birthday and it is Mary's middle name, but that mightn't be enough for them to use it even as a middle name, let alone a first name...
Come on July...the suspense is going to kill me