Stop Grandma from Leaving Gas Stove On

My 94 year old mother forgets and leaves her gas stove top on. We can’t remove the stove because my live-in niece uses it to prepare meals. If my niece lives to go to the store mom will decide to scramble an egg, turn the stove on, get distracted and walk away with stove flames on high. Is there a safety on and off valve that can be installed to the in-coming gas line that requires a key or code? Is there even an on/off valve that can be accessible to my niece and not my mother? Any suggestions? Thanks.

You can install a child safety knobs protectors which you can buy in a hardware store.

Gene.