The button on her wrist or around her neck helps only if it has charge, reaches the places where she actually falls, and rings a phone that someone can hear. Most of that work happens on an ordinary day when nothing has gone wrong, so pick that day now.
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.
Test it where she falls
Stand where she stands. Sit on the edge of the bed, walk to the bathroom doorway, and press the button from each spot. Use the device she actually wears, not the one still in the box. Check that the call connects, that the person answering can hear her, and that a collar, sleeve, or bathrobe is not covering the speaker or microphone. If the signal fails at any spot, write that spot down, because the route needs a second plan there.
Check the charge on a fixed day
Choose one day each week and read the battery indicator before anything else. Charge it the same way every time, in the same place, so the cradle does not wander. If the device has to come off her body to charge, decide who removes it and who puts it back on, and write that person's name beside the charging day. A button that is off her body overnight is not protecting her overnight.
Read the water and fall settings
Look at the label or the manual for the water rating. A unit rated only for splashes should not go into the shower, and the shower days need their own plan. If the unit has automatic fall detection, find where it is switched on and decide whether to keep it on. Treat it as a backup. Automatic detection can miss a fall that looks ordinary, and it can ring when no fall happened, so she still needs to press the button herself whenever she can.
Check the strap and the clasp
Once a month, run the strap through its clasp and look at the loop, the pin, and the stitching near the device. Replace a strap that is cracked, stretched, or loose enough to slide off a hand. A device she has taken off to get comfortable is not one she can reach at 3am.
Name who answers and who keeps it working
An alarm is a chain of people and parts. Write down the phone number that receives the call, then make sure that phone is charged at night and loud enough to wake a sound sleeper. Name one person who owns the device: who calls the company, who arranges a replacement when the battery or unit fails, and who runs the monthly test. Ask the company, in writing, how long the battery lasts, what happens when it runs low, how a replacement is handled, and what the monthly service covers. Keep that paper with the device so the answers are there when something stops working.
Questions about her falls, her balance, or whether any of her medicines play a part belong with her physician, not the device company. For the first steps after a fall, see the local help page.