One day overstay what problem do I have to face

Shiela, the stay duration counts from May 1, so if your daughter leaves on May 31, she will overstay by one day. However, your daughter can choose to extend the stay duration or not. According to the feedback of someone, usually if the duration of the overstay is less than 3 days, they will give you a written warning for first time offence. He overstayed for 24 hours and were given a written warning by the immigration and told not to repeat again and he was free to go. By the time when he returns to china the next trip everything was ok. There were no stop or check by the immigration. But this is just for your reference. I still advise you to extend the stay duration or your daughter can check in on May 30.