Yeah i ask that question ti myself also

Netavin, thanks for kindly replying. I think the experiences of Sarah and Jacob’s sons can help us to understand. When Sarah asked Abraham to protect her and Isaac from persecution by Hagar and Ishmael, Abraham protected them. But when Jacob didn't protect Joseph from his jealous (and murderous) half-brothers, God saved Joseph by relocating him to Egypt. So, perhaps Hannah realized that Elkanah wasn’t going to protect her from Peninnah’s persecution (but was instead making Peninnah more jealous by showing favoritism to Hannah (1 Sa 1:5)) In that case, Elkanah also seemed unlikely to protect the yet unborn young Samuel from Peninnah’s jealous (and likely to become murderous) sons. So, to preserve Samuel’s life, Hannah prayed to God to relocate Samuel to Shiloh. I think God recognized that doing so would protect Samuel, and it would also provide a replacement for Eli’s wicked sons. So, I think that when God prioritized saving Samuel’s life over the requirement for parental training of Deut 6:7, the result was not an ideal situation, but it was as good as it could have been considering the imperfect people involved. From this story I think we can also see aspects of God's love for his own precious son, Jesus. How does that sound?

Because she promised to God, when God blessed her with a son, she will give back to God, that's why she need to do like what she has promised to God. Hannas have faith with God.