Wait, I thought Washu could become a cabbit too; been a while, so might be misremembering things.
No. the cabbit is an engineered ship-girl bioform she created.
Also, there are multiple continuities due to the company who owns the rights making a bunch of spin offs with the same characters but completely unrelated plots that were completely unrelated to the original plot.
Only the OVA and manga are canon as it was done by the original author.
As for Washu... she is one of the 3 creator goddesses who created the local multiverse cluster (with a subordinate god in each universe reporting to them) as an experiment about whether it is possible for a man to ascend to their level.
Tokimi fostered endless wars to try to trigger ascension through conflict.
Tsunami turned herself into a tree and self polinated to create an entire race of demigod trees who are sapient and magic. who in turn bond with humans of the Jurai royal family. Their spaceships are literally a tree in a pocket dimension using divine reality warping for everything a spaceship should do. They are the most powerful military in the galaxy and the only reason they didn't conquer it is that the trees are pacifists.
Washu sealed her own memories and gave herself a compulsion to delve into SCIENCE to the extreme.
Early on she fell in love with a mortal man. But he came from an ultra wealthy family with "old money" beliefs that forced them apart and even forcibly took legal custody of her daughter.
(said daughter ends up being the very distance ancestor (20,000 years before show starts) of Mihoshi)
As a result of this, washu decided that "being an adult suck / adults suck" so she shapeshifted from her natural bombshell milf body into a young tween body and is just play acting like a child. She is an adult play acting, although not due to it being her fetish. But due to PTSD with "adult society".