A switch she can reach from bed lets her turn on light before she stands. Replacing or moving one is electrical work, so the order matters. Decide the location, check the box and wire, cut the power, and only then touch the switch.
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Step one: place the switch
Sit in the bed in her usual position and reach toward the wall where the switch would sit. Note how far her hand travels and which direction she turns. Mark the spot lightly with painter's tape. A switch placed where she can reach it from the bed works better than one placed where it is easiest to wire.
Step two: check the box and the wire
Find out whether the wall has a box at the spot you marked. If it does not, a new box and cable run is a different job, and it usually belongs with a licensed electrician. Check with your county or city building office whether the work needs a permit in your area, since the answer decides who is allowed to do it.
Step three: cut the power and prove it is off
Find the breaker for the circuit, turn it off, and label it. Then use a voltage tester on the existing switch wires before you touch them. If the tester shows power, stop and call an electrician. Do not rely on the switch position alone.
Step four: swap the switch
Photograph the existing wires before you disconnect them. Match each wire to the same terminal on the new switch, following the diagram in the new switch's instructions. Confirm the ground wire is connected. Fold the wires into the box carefully so none are pinched, mount the switch, and fit the cover plate.
Step five: restore power and test
Turn the breaker on, then test the switch from the bed. Turn the light on and off three times from her spot, and check that the light responds each time. If it flickers, buzzes, or does not respond, cut the power again and call an electrician.
Decide when to hire
Hire a licensed electrician if the box is missing, the wires are old or brittle, the tester shows power, or the circuit shares other fixtures you cannot isolate. Ask for the scope in writing and whether they will test the switch from the bed position.
Write it down
Note the breaker label, the switch location relative to the bed, the date the work was done, and who did it. Keep that page with the house papers, so the next person knows which breaker to cut.