PTL The POWER of PRAYER is MARVELOUS!
Thankfully, It does work, your sis has positive proof.
RE: PSALM 91
Our family has seen the promises of protection on more than one occasion.
Maudeen slipped outside during an ice storm and was unable to get up. Miraculously she got her footing and told me later that day that it her leg was sore when she walked. She continued doing whatever needed to be done, going up and down stairs, etc. Years later she had an x-ray done on her leg and the doctor told her it had been broken and had fused together perfectly.
Another time my mom fell backward while using a walker. No one could get to her in time to catch her. The caretaker said Mom literally floated to the floor and landed in a position that was easy for people to lift her back up. (She had two hip replacements).