Start in the dark, in the place she actually sleeps. Stand where her feet would touch the floor when she sits up, and find the light switch she would reach for first. Many houses put the switch by the bedroom door, which works for someone walking in with the light already on. At night, it may be the first thing she has to find with a hand that is not yet steady.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Measure the reach, not just the wall
Run a tape from the edge of her bed in a straight line to the switch plate, and write that distance down. Then measure the height from the floor to the center of the switch and write that down too. Take both measurements with her bedside table and chair where they normally sit, because the table often blocks the line you would otherwise draw on paper.
Now check the switch against the trip itself. Does it sit on the side of the bed she would get up from, or on the far side? If the only switch is across the room, that is a fit problem before it is a lighting problem. Note whether she would have to step onto the floor to reach it, and whether a hand on the bed frame or nightstand could get her there first.
Walk the six stops with the light off
Do this part with another adult standing by, and keep the path clear of cords and shoes. Walk bed to bathroom in the dark, pausing at each stop on your floor plan. At each stop, ask what she could see only once the light was on. The door hinge, the rug edge, the step down into the bathroom, and the toilet seat are the usual places where a shadow hides something. Write down every stop where you could not see the floor clearly.
Choose the light that fits the gap
There are three common answers, and each one needs a different check. A switch moved closer to the bed is an electrical job, so get the family and a licensed electrician to agree on where it goes before anyone drills. A plug-in light near the route needs its cord measured against the walk, so the cord does not become the next trip hazard. A motion-sensor light in the hall needs its range tested on the actual walk, because a sensor that only turns on after she has already passed the door is not doing its job. Ask the installer to show you the light at the bed edge and at the bathroom step before they leave.
What to write down
Write the bed-edge distance, the switch height, the stop where you lost sight of the floor, and which light option you chose. Put the day on the note in your own record, and add one line in her own words about what she said she could see on the walk. If she has dizziness when she stands or new trouble seeing in low light, take those questions to her doctor. A tape measure can show you where the light is, but her doctor decides what is causing the problem.