The second fall, or the bruise on her arm that she cannot explain, and the walker still standing in the closet where it has been since the hospital sent it home. Before this becomes a nightly argument, it is worth knowing that the walker was never really the goal, and that the fight over it is aimed at the wrong target.
Before you say one more word about the walker, notice what is rising in you, whether it is the fear that the next fall is the bad one or the anger that she will not just use the thing. That is yours, it is normal, and it is worth one breath before you start.
Before the falls become a character trait, rule out what an appointment can change, since new medications, blood pressure drops on standing, worsening vision, and foot pain all knock people down and all have fixes. A fall has a cause, and "she's not careful" is never it.
When she refuses the walker, she is not refusing safety. The walker announces the disease to everyone who sees it, and she can hear the announcement even when she cannot say so, which means what she is defending is not a preference about equipment but her standing as the woman who has walked on her own two feet all her life. That is worth taking seriously rather than talking her out of, because it is also worth knowing what the walker honestly offers. The device by itself is not proven protection. A walker that is the wrong height, or was never fitted to her, or that she was never trained on, asks her brain to manage one more thing while walking, and managing things while walking is exactly what dementia makes hard. The one in the closet, used resentfully or wrongly, may not be the safety you are fighting for.
Which is why the real goal is not winning the walker argument. The real goal is a physical therapy falls evaluation, where a professional watches her walk, finds what is actually making her fall, and either fits and trains her on the right device or recommends something better. You stop being the walker police, and become the person who booked one appointment. The stakes are worth that appointment, since falls are the leading cause of injury death in older adults, and a bad fall is one of the most common reasons a person leaves her own home for good.
Print the one-page log if you want somewhere to keep this, and take it to the appointment.
This is what the tracking is for. A dated list of falls, and what she was doing when they happened, is what turns worry into something a therapist and a doctor can act on.
The measure of this is not whether she used the walker tonight. It is whether she still takes your arm, and whether the appointment is on the calendar. Those two things are yours, and the rest belongs to the therapist.