Sara is suffering from post-traumatic stress. The birth of the twins was too trying for her. She did not have enough psychic resources to deal with the new family situation. Is it possible to let the father take care of the twins at night, so Sara and her mother can be together? Sara needs to be a child, to drink milk with the baby bottle if she wants to, to sleep with her mother and to have her mum only for herself. A two-year-old child seems big compared to two infants, but she is a very little human being.
During the day, Sara should eat only when she is hungry. She must learn to listen to her own body and eat when she is hungry, and stop eating when she is satisfied. In some cases, the child's hunger will coincide with the family meals, but this is not always the case. Sara may not be hungry when the family meals are served.
You should try as follows: put good and healthy food in small appetizing pieces in Sara's room. Try not to care about what happens next, and let her eat when she feels hungry.
Her eating habits should be a relation between her hunger and food; you should be involved as little as possible. She will not starve to death. If there is some good food at home, she will eat when she needs it.