In the manga her story is much different, and has a lot more drama. It turns out that Nyanko, and Luna &Artemis were from the same planet.
In the manga Nyanko disguised as a student tried to befriend Usagi, and tried to get her to stay away from the starlights. Luna and Artemis detected her soon after because of her being from the same planet, Mau.
In the future, Diana, which was standing gaurd of the time space door for pluto, sensed something, and got permission to go back to the past. When she got there, Luna and Artemis were having a showdown with Nyanko. Diana tried to get them to stop fighting, but Nyanko would not listen. Nyanko said the cats were traitors for leaving the planet, and the cats said she was the reason for many deaths on their planet just for power from Galaxia. She tried to blast them, but Eternal moon blocked it. Finally she hit Diana turning her into a normal cat, and eventually Luna and Artemis too. Nyanko fled when Starfighter attacked her, but she was not saved by galaxia when she got back to the place. By taking her bracelets, Nyanko was no more.
~Back to Nyanko's Shrine~