Nah, she kept the immortal serpent body. And the Empire. She did what she could throughout history to "tweak" it into a less evil empire without making it seem less evil, and then once she reached the "present" she was fully free to get down to fixing its social ills much more fully. And it was very useful having an empire's resources to help us deal with the other big bads, especially the omnicidal faction that was trying to destroy reality altogether.

It's fortunate that throughout the whole campaign my character kept facing challenges to her fanatical devotion to her personal philosophy and coming through them more confident and grounded in it than ever. That preparation allowed her to remain steadfast to her goal throughout those 1500 years.

Oh, she did occasionally use a variant of disguise self to pass as her original pre-Serpent Queen self from time to time after that, to stay on the thread's topic. But as I recall we had to houserule it a bit because I don't think disguise self can normally make a size-large serpent look like a size-medium humanoid.