A round knob asks her to grip, twist, and pull at the same time. A lever asks only for a push or a pull with the forearm or the palm. Swapping one for the other is a small job that can change how easily she moves through a room. It can also go wrong if you buy the wrong size or force a latch. Work in this order.
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Step one: identify the door and the lock type
Look at the door before you shop. Note whether it is an interior passage door, which has no lock, or a privacy door, which has a push-button or key lock on one side. Check whether the handle uses a spindle that passes through the door and whether the latch is a standard tubular latch. Take a photo of the handle, the rose, and the latch plate. You will compare that photo against the package.
Step two: measure the backset and the bore
The backset is the distance from the door edge to the center of the hole where the spindle passes. Measure it with a tape before you buy anything. Measure the bore diameter too. Lever sets are sold to fit listed sizes, and the package will say which ones it fits. If your measurement falls outside that range, do not force the set onto the door.
Step three: swap and test
This is a mechanical job, so start with the old handle in place and the door closed. Remove the screws that hold the knob, pull the handle off, and keep the parts together in a dish. Fit the new lever's spindle and screws, tighten them by hand first, then finish with a screwdriver. Test the latch by pushing and releasing the door several times. The latch should retract smoothly and the lever should return to level without sticking. If the latch drags, the strike plate may need to move, and that is the point to stop and decide whether to adjust it yourself or call someone.
When it becomes a question for the care team
Stop and ask before you proceed if the door is a fire door, if the lock is on a bathroom she uses alone, or if the lock needs a key to open from the outside. A change to any of those is a question for the care team and the family, not a weekend fix. Keep the old knob in a labeled bag on the shelf in case you need to reverse the change.