I think it Naja's. Naja was attracted to Washu and over time harbored an unreciprocated love, who ignored all her advances and hints. Naja maybe think Washu not attracted to girls, so she goes on to make Kagato, a male version of herself that she could take over at will. While Kagato didn't inherit a love for Washu, the frustration and mounting negative emotions from Naja were gathering inside of him.

But Kagato failed to move or attract Washu, she only took him on as a student and treated him as Naja's son. Naja then stole a hair from Washu in desperation, to make Ryoko, in Naja's eyes "their" daughter - in order to complete the illusion of a happy family. This violation angered Washu and this put a wedge between them. Naja runs away and assumes new identity as "Seto" who appears on a planet at the same time Naja disappeared [official background]. Seto grows up and goes on lesbian rampage as an outlet for her previous frustrations and unreciprocated love [official background].

With no one left to pick up the pieces, Washu assumed the stewardship of Ryoko. This is why Kagato can say he "made Ryoko" but it was really Naja's Ova that made Ryoko. This is also why Ryoko has no previous memories of Washu.

Yes, I think I should change topic title. It still Washu's daughter in technical sense, but more like how Mayuka was Tenchi's "daughter."

We need those Novels Animated, it would make so much more make sense, especially things like this