Rebound without paxcovid ?

My mom with multiple sclerosis(58F, 5 vaccinations) is having issues with her infection. She tested positive on 12-02, got better around 12-08, and by better I mean no more symptoms, and now is experiencing mild shortness of breath, sore throat, fatigue and a dry cough on 12-11. I read that rebounds usually happen with paxcovid but she didn’t take any and her doctor is really no use on what to do. Is this a dangerous situation and what can be done ?