Sounds like your mom cares about the health of your cats and doesn't want to see them suffer. I'd get rid of the plant.
From:
https://dailyxcoffee.blogspot....
"Unfortunately, the coffee plant contains saponins, toxins known to cause irritation of the skin of the cat or of its oral cavity and of the gastrointestinal tract if the toxin is eaten. Your cat may be exposed to these toxins or locally, if it rubs against the coffee tree, or by mouth, if it chews or eats a part of the tree. Symptoms include contact dermatitis (rash), vomiting, loss of appetite, depression, fatigue, general weakness and rapid heartbeat. Although coffee poisoning is a rare or life-threatening complication, it is still essential to take the cat to the vet for medical treatment as soon as possible."