In the Inverted World, Philomena was ultimately not Paris's High Priest. Once she confirmed that Paris was entering the Underworld Great Tomb, she resolutely protected him by standing in front of him and took on the task of covering the rear.
To guard against any sneak attacks from behind, she would guard the entrance and wait for Paris to return victorious.
She put it nicely, not wanting to die inside with Paris.
Paris wasn't reluctant either; he spread his thoughts to scout ahead and soon disappeared from Philomena's sight.
Philomena had said she would guard the entrance, not letting even a mouse get through. Once Paris was far enough away, she chose a nearby sewer to hide in and concealed her presence, effectively becoming invisible.
Her invisibility was fake, but Paris's was real. He took out the gift from his father-in-law from his Personal Space and put it on right away.
The Shadow Cloak!