https://rsport.ria.ru/figure_skating/20171120/1128921192.html
This article describes the nature of Anna's injury, as well as describing the circumstances under which she withdrew in Yoshkar-Ola. Based on google's rough translation: Anna could barely move after the competition, and was hardly able to take off her skates and costume in the locker room. Although it's unclear from the description (inflammation, irritation of the nerves, inability to move), it sounds like she has a slipped disc (I have no idea what "clamped ligaments" could mean, but her symptoms sound like the ones I have and I have two slipped discs in my back).
The article also says she did not go to the doctor after Canada, and was working on her choreo and doing physical therapy, but got sick and resumed training harder after and her back flared up again.
... I really hope if she has not yet gone to the doctor since Canada that she goes now. These back problems are serious, very serious. This is the sort of thing you carry for life if you don't treat it properly, and I say that from personal experience. I hope she takes up the fed's offer to treat her abroad so she can get back on track.