You don't need to generate another large picture with AI for the nude sprite. The nude sprite will be small and easier to edit by hand with an editor. So, you can use the dialog picture you had AI generate, make a copy for editing, shrink it to around 32x32. Change the pixels so it looks nude. That way it looks like the same character and the pose is the same.
For facial expressions, you'll probably want to find an AI that can use 'inpainting' or 'iterative editing' on the generated image.
An example the dev gave several releases ago was an AI called Flux Kontext:
You can probably use this to help with the facial expression to make it easy.
