What should I do when a friend exhibits severe body dysmorphia on social media?

At several points in my life, I had a valued friend who seemed otherwise rational and grounded, but who also exhibited dangerous body dysmorphia on social media. In these cases, the friend would first go through a several-month phase of confessing to several psychological problems, such as fantasizing about suicide and of cutting herself with a blade. This friend would then sternly add that she has since recovered, but would admit to still feeling that her natural physical features are ugly and deformed. Then, months later, the friend would go into another phase. On social media, in front of many other people, she would make brazen gestures indicating body dysmorphia, such as uploading photoshopped pictures of herself as a corpse ready for burial or saying that she planned to starve herself to achieve her ideal of being skeletally thin. A major problem was the reaction from our online mutual acquaintances. Some admitted that they saw these problems, yet they acted like the friend was behaving normally. Others outright complimented the dysmorphic imagery and statements. In these cases, I think that my friend knew that her body dysmorphia was dangerous. She put it on display so that others would normalize her pathology, because then she could more easily rationalize her behavior as harmless. That seems really dangerous, but what is the proper alternative? How should people respond when a person puts his pathological self-destruction on display?