Her hand goes to the sink at night more than you would guess. She uses it to steady herself on the way back from the toilet, then reaches for the cold tap or the hot one with whatever grip she has left. If the sink has the old two-knob style that needs a firm grip and a quarter turn, that reach is the wrong shape for the job. A single lever she can push or pull with the side of her hand is easier to work in the dark, and most people can finish the swap in one Saturday with basic tools.
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.
Check what you actually have before you buy anything
Look under the sink and at the faucet body. A single-lever replacement is made for a specific valve type, so you need the brand, the model number if it is printed on the faucet or the old handle, and the type of cartridge or valve inside. Take photos of the handle, the trim plate around its base, and the valve under the sink. If you cannot read a model number, bring the old handle to the store and match it in person. Do not buy by the look of the faucet alone.
Shut the water off and empty the line
Close both supply valves under the sink, hot and cold, turning clockwise until they stop. Then open the faucet to drain what is left in the line. If a supply valve will not close all the way, stop here and call a plumber. A valve that will not shut is the first thing to fix, and it is not a job to force.
Remove the old handle and valve parts
Take off the decorative cap or the set screw, pull the old handle straight off, then remove the nut or bonnet under it. Pull out the old cartridge or stem if your valve type has one. Lay the parts out in order on a towel so you can match them against the new ones. Keep the old cartridge until the new one is in and working. The mounting holes and the base plate stay where they are.
Install the lever and seat it
Fit the new cartridge or stem the way the instructions show, with the alignment tab or index mark facing the same direction as the old one. Hand-tighten the retaining nut first, then snug it with a wrench. Snugging is enough. Forcing it can crack the plastic on a new part. Put the lever on, set the cap, and check that the lever sits level and does not wobble when you move it side to side.
Turn the water back on slowly
Open the supply valves a little at a time, then all the way. While the water runs, watch the base of the faucet and the connections under the sink for drips. Run the cold side first, then the hot. Let the water run steady, then move the lever through its full travel. Tighten a connection only if it drips, and only a quarter turn at a time.
Test it the way she will use it
Stand where she would stand at 3am, one hand on the sink edge, and reach for the lever with the hand she uses most at night. Push it toward hot and toward cold using the side of your hand, not your fingertips. Check that it returns to off or to the middle without you hunting for the position. Then check the hot side at the tap. If the hot water runs hotter than you want for her, the setting lives on the water heater, not the faucet. Changing that setting is a plumber's call if you are not sure how it works. Start with the Local help after a fall, St. Louis page if you need someone to come out.
What to write down
Write the faucet brand, the model number, and the cartridge or valve part number. Write which valve shuts off the sink and where the main shutoff is, in case the next repair starts with water on the floor. Write one line about the test: how she reached the lever, and whether it returned to off on its own. Keep the receipt and the old cartridge in one bag so the next person who opens the sink can match the parts without guessing.
For where the facts in this desk come from, see the Sources page, and for how we write these pieces, see How we write this desk.