“She’s 68 with arthritis.”
Have her try 20 Mule Team Borax for the arthritis...buy it in the laundry section of the grocery store. Have her put a tablespoon or so in a small dish and keep it in her bathroom where it is easily accessible. She should like the tip of her index finger, stick it in the Borax, lick the Borax off...and do that 3 or 4 times a day.
Borax and expecially Boric acid are label as poisons. They are not. Borax is less poisonous than table salt. Borax also is great in the laundry, so she might find it beneficial there too.
Borax is a miracle sustance, it is also the most effective roach poison I know. I would be very careful about doing any such thing.