The £30,000 legacy to Cynthia Asquith and all the other many legacies to various people would have come out of Barrie's estate after probate and after death duties have been paid (and legal fees), so there probably wasn't much left after that. Any residue would have gone back into the estate and it would have been allocated to the main beneficiaries at the discretion of the trustees and executors.
Cynthia also inherited all rights to JMB's works (except for Peter Pan)(Clause 7), so that set her up for life as royalties were quite significant and provided her and her husband with a steady income (after her death, her children would continue to enjoy the benefit of these royalties).
Additionally, she and Peter LD were bequeathed all Barrie's furniture, manuscripts, papers, pictures, books etc (Clause 8 ) which were sold off and raised a considerable sum of money.