I've learned that when people are ill for a long period of time, prayer becomes difficult for them. That was true for my mom. She had always been a person of prayer: she went to daily Mass & said her rosary and her novenas. But when she became ill, her physical and spiritual strength both diminished and prayer become difficult for her.
Even Moses found that to be true. As long as he kept his arms raised (the gesture of a Jewish person at prayer), the Israelites would win the battle. But when he dropped his arms because he was physically tired or spiritually weak, the Israelites began to lose. He needed to men on either side of him to hold up his arms for him. When we pray for others because they are too weak to pray, we hold up their arms for them.
But we find that in our prayer for them, we are the ones who change. I learned this in the last few months when my dad's health worsened. Months of illness can make you impatient and easily upset. So I would pray for him. But what I found was that I needed to pray for myself. I asked God not to change him but to change me. And when I could become more patient with him, that would make him feel better and then my prayer for him was really answered.