That is an excellent question! Cloistered nuns pray for all people. They don't need to know about their lives. They ask God to provide them with whatever it is that He recognizes they need. All prayers are answered. The best prayers are those of strangers who seek only to ask our Lord to watch over us and guide us to eternal life with Him in heaven.
Lovely answer.
Many years ago, when I was a senior in a Catholic girls’ school, we spent a three day silent retreat at a cloistered convent in the L.A. area (which is still there, actually) and the Mother Superior came out and spoke to us (she stood beyond the altar rail). She said that in the 1920’s the at-that-time Bishop had asked her order to establish the cloistered convent in the area to “provide prayer and a counter balance to the sinful lifestyle that was glorified in the area”.
I’ve never forgotten that, and have often thought of it whenever I’ve come across some “new age” writing or belief about “balancing good and evil” or “countering evil with good”.
I very much admire the monks and nuns in monestaries and convents around the world who spend their lives in prayer (and this admiration extends to other-than-Catholic monks and nuns also).