@thecrystalrook
There is a term called "meeting of the minds." As long as there is a mutual understanding and it is stated clearly IN WRITING so as not to claim "I was confused" or "He didn't specify" later on, a chat is most certainly legally binding.
https://www.law.cornell.edu/wex/meeting_of_the_minds
Contracts have even been written on bar napkins and held up in court by notable celebrities in the entertainment industry. Certainly having something officially notarized is better and avoids headaches, as long as signatures are included (IT info in this case), anything can serve as a legal agreement. Word of mouth can even serve as a legal agreement if there are witnesses to the conversation.
You cannot simply revoke a copyright permission. It takes a lot of time in court and a lot if legal argument about why the other party wants to do this. If they cannot prove some form of legally recognized distress in the use of their property, they won't win.
The character won't have to be edited at all. If she tries to push this into court, she'll have an uphill battle involving evidence to her claims and legal fees I'm quite certain she won't want to pursue.