She hasn't needed to write for the money since about Goblet, certainly Phoenix. At least in this series it's been about finishing and personal goals. Any future project will only ever need to be about her desire to tell a story, or at least do something to fill the time between reading bank statements.
She's also already indicated the possibility of writing down all her background material, perhaps padded with existing canon descriptions into an encyclopedia (at some point): this heads down the path of keeping the existing fans happy with more HP universe.