Much of this information is in, or can be found from, the question you refer to. If you want to read everything, or just warm your feet by the dumpster fire, you can go to meta.SE. The place to start, with much of the information indexed, is Firing mods and forced relicensing: is Stack Exchange still interested in cooperating with the community?
- She has not been reinstated. SE has dug in its heels, out of obstinacy, as far as I can tell. They ignored her and the growing storm for over a month. At this point the lawyers are involved. Monica has initiated a lawsuit against SE. SE has decided they want to try to fight it out rather than compromise.
- The official claim is that she misgendered trans users. This supposedly happened in moderator-only spaces. To the extent mods can see, that did not occur. Trans mods have spoken up for Monica as well.
- Changing usernames and avatars is one way that people can advocate for her. Some users know her, others are appalled by the rank injustice on display.
- On your user page, you would go to the "edit profile and settings" tab, and change whatever fields you like (e.g., username, about me, and avatar).