Hilsenrath's appointment followed the departure of Rob Behrens whose seven-year tenure ended in March 2023.
She had previously been chief executive of PHSO since June 2023 and before that was their director of strategy.
Gill Kilpatrick, who is currently PHSO's chief operating officer and deputy chief executive, was promoted to interim chief executive following nine years at the organisation.
Hilsenrath said: 'I am immensely humbled and honoured to be selected as interim ombudsman.
'My predecessor, Rob, has left an extraordinary legacy of passion for public justice, dedication to improving public service and driving transformation within PHSO itself.
'It is a privilege to build on the work that has already been done. Alongside Gill's appointment as chief executive, and with Karl Banister as the deputy ombudsman, we have a strengthened leadership team with the appointment of a new director of strategy and a chief digital information officer to achieve our ambition of being a leading ombudsman service. We all look forward to continue delivering a service that helps those who have been let down by public services access the justice they deserve.'