Some issues I only just thought of about the use of Henrietta as a first name...If Mary does use it, she will probably have to discuss it thoroughly with her family (Jane Stephens, Patricia Bailey, John Donaldson jnr and John and Susan Donaldson) because by using it as a first name it will be as if Mary is claiming her mother Henrietta as her own...but the truth is Henrietta was also the mother of Jane, Patricia and John, not just Mary...and how will her father feel calling his little granddaughter by the name of his late wife and how will Susan feel using the name of her husband's late wife (will it be uncomfortable or is Susan a big enough person not to be affected by that aspect)...
I would love Mary to use Henrietta as a first name but it is not only up to her...her Australian family have to consent a little bit because it will then make their mother's name public property...I know it will be a definite middle name but a first name would be great, because it is a royal name, and it is such a great name and it is a way her mother can share in some small way with Mary's happiness...
Her mother's nickname was Etta...but I think if they use it they might be more inclined to use something different like, Princess Henny or Princess Hetty or Princess Hanna?