"Superior Court Rules - The Probate Office
Order 79
4. The Probate Officer shall not allow probate or letters of administration to issue until all the inquiries which he may see fit to institute have been answered to his satisfaction. The Probate Officer is, notwithstanding, to afford as great facility for obtaining grants of probate or administration as is consistent with a due regard to the prevention of error or fraud."
Until it's established in fact whether or not the lady in question does have a valid will of the deceased, and is the executrix, it seems the nephew had no choice but to seek Court authorisation to make the necessary enquiries.
It seems to me she had no obligation to the nephew when he started his enquiries, but now that she's been joined as a notice party, she has obligations to the Court.