A visitor can open websites on your guest Wi-Fi, yet the print dialog cannot find the printer. The printer may be perfectly healthy. Internet access and permission to reach another device in the house are separate questions.
Draw two boxes before changing settings
Label one box “main network” and the other “guest network”. Put the printer and the visitor’s laptop in the box they actually use. Check the network names on the devices rather than guessing from their location in the room.
Now try a harmless one-page document from your usual computer on the main network. If that fails too, first investigate the printer’s own status. If it works, the difference between the two network paths is worth examining before reinstalling drivers or resetting the printer.
Sharing controls differ by router
Google’s guest Wi-Fi instructions include a Shared devices selection, with printers among the examples. The network owner can choose what guests may use. Check the current app and your supported hardware rather than expecting every router to offer that list.
The TP-Link Archer A7/C7 guide illustrates a different distinction: guest-to-guest communication and guest access to the local network are separate options. Allowing the latter is broader than selecting one printer. Read the scope of the control before enabling it.
Choose the smallest useful change
For an occasional print job, it may be simpler for the owner to print the agreed document from an already authorised computer. For recurring use, the owner can investigate a documented printer-sharing option for the exact router model and firmware.
After an authorised change, send one non-sensitive test page and confirm which physical printer receives it. Check that the setting shares what you intended, and remove any temporary exception when finished. If the printer still does not appear, consult its model-specific discovery instructions. A working guest internet connection alone cannot tell you which local printing features will work.