What is surprising is that there are no short videos by Tiffany and no pinned comment. If she is fine physically, (the 'no big deal' scenario), then it is clear that Tiffany has zero regard for her subscribers. Feeling fine, having time to delete comments, yet not writing even one sentence of update is just Tiffany being egotistical and demonstrating her disregard for subscribers, some of whom are health professionals, elderly folks, and cancer survivors or people with cancer.
If Tiffany really is in a bad situation with another lung metastasis, then I understand her absence. She probably wouldn't know what to say. In this case, she would be a psychological disaster and would need time to go through the stages of grief, with emphasis on 'why', denial, and anger being her predominant states of mind. She probably would move back in with her mom in order to spend the maximum amount of nice days with her and close to her sister and niece and nephew in Croydon.
I don't think she would stay in Tunbridge Wells with Matt if she got the 'ultimate' diagnosis.