There is a seasonal element in play here. There is a staffing crisis at Dutch Bend. Catty Library is closed but there are staff in there unpacking boxes ready for an unspecified opening day which is almost certainly going to be postponed because all the putty's fallen out of one of the new windows. You or I, being unthinking amateurs in the ways of the public library, would send one of the staff from Catty to Dutch Bend. Especially if we were Julia, who is both on site at Catty and responsible for both libraries.
Unfortunately for Frog, he's the one who's picked up the message and relayed it to Julia. Who tells him to ring personnel for the 'phone numbers of any staff who may not be working today so that he can ring round for cover.
Mary rescued him in the end: Lippy's going to work extra hours and do the necessary.