There are many people in Thai hotels.

You are not allowed to live with three adults and one child. There are three adults in the other room. Why can't the other adult stay with her in a nearby hotel for one night? At the same time, communicate with the hotel to see if there is a room for the next day. If not, stay with her. There is nothing inconvenient.

The extra bed fee can't be wasted. You can try to communicate, but the hotel is unlikely to refund this money.