On the hair/toilet thing, two possibilities spring to mind, and they're not necessarily mutually exclusive:
1} She saw that her actions were making you upset, so she decided to do something to make you happy.
2} She decided to use the toilet as a distraction/redirection away from the shampoo event.
Remember - kids this age are discovering their own power in general, and specifially/especially the power of their own independence. All they're experienceing from their perspective is the rush of raw power. They have no context as to what it all means until you provide it for them. That takes time, and that will drain you sometimes, but that's the gig. My spmpathies, best wishes, and congratulations, all as needed.
Do you have any idea about why she seems so uptight about shampooing? Did she have a bad experience at some point, like shampoo or water in the eyes? That "no more tears" stuff is true as far as it goes, but that's not nearly as far as they want you to believe...
Ways to make it fun - Has she watched you shampoo your hair? Has she seen the Tegrin guy? The Great Gazzoo? Speed Racer? Shampoo suds make for a great helmet, and helmets are fun!
If that fails, show her pictures of head lice...
Ok, I joke, but hopefully not so much as to obscure the point.
Live for today, but get enough rest for tomorrow.