In order to be effective in praying for your adult child, you must stop blaming yourself for everything that goes wrong. Give God a little credit here.
Although there are different stages and seasons of parenting responsibilities, your heart and mind will always be with each one of your children for the rest of your life. And this is no easy task, for no matter where they go or what they do, a part of you goes with them.
When we observe life happening to our adult children in a challenging way, we want to help them. But how much is way over board, and our little is not enough? Only God knows the answer to that question.
Prayer is not telling God what to do. Prayer is partnering with God to see that His will is done. You don't have to fully understand what God's will is in order to pray that His will be done.
There are only two ways to avoid guilt as a parent. The first is to die soon after your child is born. The second is to walk with God every day and ask Him for wisdom about everything.