In the middle of the novel The Poet X, why does Xiomara get a harsh punishment from her mother?

In The Poet X, Xiomara is punished by her mother in the middle of the novel after she arrives home late one evening after missing her stop on the train. Xiomara is romantically involved with Aman, which is the exact opposite of what her incredibly devout Catholic mother wants.
When Xiomara arrives home late after she was so caught up kissing Aman that she missed her train stop, her mother reacts furiously and grounds Xiomara. Xiomara is only allowed to go to school, church services, confirmation classes, or be at home. Her mother takes her cell phone away as well, further isolating Xiomara and straining her relationship with her strict mother. Xiomara eventually is able to leave the house again and regain her cell phone.