Not Kagato. The woman that Kagato was cloned from; Naja Akara. She was Washu's best friend through the Academy, and "died" a few decades before ryoko was created/born. If you look carefully, though, Naja and Ayeka and Sasami's grandmother, Seto, looks -exactly- like Naja, only her hair is light green instead of silver. But their eyes are identical, and Seto was discovered as a child on the planet Naja was killed on.
Part of the reason that Dr. Clay hates Washu is because of her friendship with Naja. Clay tried and failed many times to ask Naja out, but, to be frank, she hated his guts. XD She is even noted to have kicked Clay into a campus fountain on Washu's first day at the academy.
[link] Naja in her academy uniform.
[link] naja and washu watching massive destruction after Naja surprised Washu as she was testing her first self-made weapon of mass destruction. This is referenced to in Tenchi GXP as "Washu's Hole" or something similiar.
[link] naja, washu, and her hubby and son!