I don't know. When I was a jw I would pray for my husband's abuse to stop, and the only time it did was when I left. Was that an answer to my prayers, or was it just me taking action?
After being df'd I stopped praying for several years, until I visited a "worldly" friend of mine from childhood who was dying from brain cancer. She was a big born againer, and during a tearful conversation, she asked me to pray for her. She wasn't afraid to die and was firmly convinced that she was heaven bound. But she wanted to see her only child off to his first year of school, to let him out into the world. so to speak. The doctors told her that it would never happen, as the tumor was inoperable and growing larger by the day. I also told her that it wasn't me she should want praying for her. She was very familiar with the jws and my df'ing and said, "You are exactly the kind of person I want praying for me." It was so touching, so I prayed and prayed. She called me a few weeks later to say that the tumor had stopped growing and thanked me for my prayers. She died peacefully six months after her son started the first grade.
I prayed ferverently for my dear Aunt Shirley, but she died after being in a coma for four months, just three days shy of her 60th birthday. Did she die, because I waited until she was in a coma to pray for her? I don't know, but I certainly hope not. I went through months of agony and anger over her death and then our beloved cat disappeared. I prayed and prayed and prayed, even making my husband get on his knees every night with me. He thought it was ridiculous, but as usual, he humored me. The mailman brought that crazy cat home to us seven days later, finding him sick and wandering the street in front of our house.
Sorry to say, I don't have a sure answer for you. I do pray now more than when I was a jw, and I don't have near the hassles and heartache that I did then. I guess it doesn't hurt to pray, as long as you can handle the disappointment of your prayers being answered. It probably also wouldn't be a good idea to let prayer take the place of taking action.