A walker that fits well in the store can still be wrong for her in the bathroom. Height matters, but so does how she stands, what shoes she wears, and whether the walker can turn where she needs it to turn. Fit the walker with her as she actually moves, and then test the trip from the bed to the toilet before you call the setup finished.
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Fit the height with her standing
Have her stand tall in the shoes she wears at night, with her arms relaxed at her sides. Set the handles so they line up with the crease of her wrist when her hands hang naturally. Her elbows should bend slightly when she grips the handles, not lock straight and not fold sharply. If she is unsteady, have someone stand within reach as you adjust, and keep the walker close to her body. A physical therapist or the provider who supplied the walker can check the fit, and that is the right person to confirm it because her posture and balance are part of the answer.
Test the trip, not just the grip
Have her sit on the bed, stand up using the walker, and walk the full route to the toilet at her normal pace. Watch whether the walker catches on the doorframe, the bed corner, or the edge of a rug. At the toilet, have her turn and sit down. Check that the walker stays close enough to reach when she needs it again. If the turn is tight, the cause is often the walker's footprint or the open space beside the toilet, not her ability to turn.
Measure the room before you change the walker
Measure the clear floor space at the toilet and the width of the bathroom door. Compare them with the walker's width and turning space. If the room is tight, a narrower walker may help, or you may need to move the bedside items that narrow the path. Do not assume a shorter walker fixes a turning problem. Height and footprint are separate questions.
Write down the setting and the owner
Record the handle height as a measurement from the floor, the shoe type used for the fit, the date of the adjustment, and who made it. Note the bathroom door width and the clear space you measured at the toilet. If someone else uses the walker or it moves to another room, the next person can check it against these notes instead of guessing.