Naomi, of course, was still human. Once Elimelech died, she could have gone back, but she'd stayed in Moab. The first word of verse 7 - “Wherefore” - shows that it was because there was finally bread in Israel that she went back.
There are numerous reasons she may not have returned earlier. Women couldn't fend for themselves by getting jobs, etc.. Also, she may have felt it was not yet time to insist on Orpah and Ruth following her and turning to God. For all we know, her waiting on God to end the famine may have been a sign of what would later show as her bitterness toward God, and not trusting Him totally, after the loss of her husband and sons. The Bible only tells us what God, in His infinite wisdom, knows we need to know. And, He knows we don't need to know the exact reason Naomi waited till there was bread.
However, she had, at least, been waiting. She'd had faith God would help and protect her, and her family. And, she'd known God could provide bread, allowing her to return. Naomi was human, but had shown enough faith that Orpah and Ruth believed with head knowledge about Him.
The question was, would they believe with heart knowledge. Because, in those days before the Holy Spirit came to live inside believers, they would have to dedicate themselves to following God. Salvation was still by faith. But, it was faith that God, in His divine mercy, would forgive them when they failed to keep the whole law, remembering they were but dust. (Psalm 103:14) It was faith that the sacrifices made would cover those sins, till that day when the promised Messiah would wash their sins away for good. In the same way, Abraham had believed, and God counted it to him for righteousness. (Gen. 15:6)
