The fan in your mother's bathroom is loud, rattling, or has quit, and you are about to find out how much of a bathroom lives above the ceiling. A fan swap has four handoffs: the measure, the install, the electrical check, and the test and sign-off. Each one needs a named owner, or the gaps will be where the trouble shows up.
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Handoff one: measure and match
Measure the existing opening and housing, and check the duct size. Note where the duct exits, the switch that controls the fan, and whether the unit combines a light or heater with the fan. Take photos of the attic side while you can see it. Look at where the duct ends. A fan that vents into the attic instead of outside can cause moisture problems, and a duct that is open or disconnected needs fixing before anything else. The owner here is the person who has been up in that space, so say who that is.
Handoff two: the install
The install covers removing the old unit, adjusting the ceiling opening, mounting the new housing, connecting the duct, and sealing the exit. Ask who patches the ceiling afterward and whether that patch will be left ready for paint or finished by someone else. Paint touch-up is a separate job, so decide now whether it is part of this one or the next one. The owner is whoever is doing the install, and the patch owner should be named in the same breath.
Handoff three: the electrical check
The new fan may need a switch, a new wire run, or a connection to the light circuit. If the wiring has to change, check your local rules on who is allowed to do that work, and make sure the person doing it is qualified. Ask the installer to confirm the switch works and which switch controls which part, such as the light, the fan, or a heater. Write the switch map down, because nobody will remember it in six months. The owner is the licensed electrician or qualified installer your area requires.
Handoff four: test, sign off, and the written note
Test with the door closed and the fan running. Hold a tissue or a thin strip of paper near the grille and see whether it pulls toward the fan. Listen for rattles. Run the light and any heater. Check that the exterior flap opens while the fan runs. Then ask for a short written note with the model, the switch map, and what was patched and by whom. The owner of this handoff is you or your mother, not the installer alone, because you are the one who will be calling if it goes wrong.
The dull part that causes trouble
Grilles collect dust and lint, and a fan that was quiet on install day can start to sound like a jet after a year of neglect. Put a grille check on a calendar, not in your head, and give it an owner. That small line item is what keeps the new fan from becoming the next thing you are awake about at 2am.
The fan will not thank you, and the ceiling will not either. But the bathroom will stop sounding like a runway at six in the morning, and you will have a page that says who did what.