Will anything I entrust to God be lost, and will a girl's prayer to marry a specific person be lost after she has become attached to him and her religiosity has changed due to her mother's refusal of this marriage?

The questioner is advised to strive to return to acts of obedience and supplication, and to ask Allah to grant her marriage to a righteous man. She has done well by agreeing to marry the other man to please her mother. There is no blame for the hatred that arose in her heart towards her mother, because matters of the heart are not within human control. However, she must avoid any bad behavior towards her, and if it occurs, she must repent and seek her mother's forgiveness. She should ask Allah to grant her success in marrying someone who is good for her, or perform Istikhara (prayer for guidance). A mother's insistence on her daughter marrying a certain person is not considered oppression; rather, it stems from her belief in what is beneficial. Forgiving the oppressor is a great act of nearness to Allah, especially when it is one's mother.