Late periods. And what should she do?

My girlfriend had been fairly regular for 6-7 months till December 2019. She was expecting her next period on 4th January 2020 but it didn't come for 15 days. There is no chance of pregnancy as I've already confirmed with various doctors on practo. She went to her gyanaecologist and she gave her regestrone tablet for 3 days. She took just one tablet that night and next day morning she got her period. It was a normal period lasting 4 days. Later she fell ill with UTI and she was on antibiotics for 2 weeks. During her UTI, she had her pelvic sonography done which showed her endometrium was normal and 8mm thick. She had a little bleeding during her UTI. Now she is well but she expected her period on 17 Feb which has not yet come. She is having all the symptoms like pain in the waist and white discharge and mood swings. When can she expect her period to come and what should she do?