S.H.
yes, this is a phase. & with many of my daycare families through the years, I've had parents tell me similar stories about this & with grass/sand/etc.
What I have found is that this is not an issue at daycare....simply at home with the parents. Little ones will flip & twist you as often as they can. So, in addition to all of the other good ideas posted, I'd like to add one more thought: instead of catering to her by buying new boots....what would happen if you took her outside & let her see YOU splashing & having fun in the wetness? What would happen if you just cut loose & used fun/humor to pop her out of this phase? Instead of babying her? You could even "wash" the boots in the tub to show her how absolutely o.k. it is to get wet!
I fully realize many Moms are cringing & thinking WTH is wrong with this woman! But, it works. When little ones complain about water on their shirt, a fly on the wall, mud on their shoes.....I just clap & say "hooray! Let's look at it". I then become a Drama Queen & point out all kinds of cool details.....it gets the kids interested, it diffuses the Boohoo Baby, & the kids gain a little knowlege in the process.
Fun beats Finicky....everytime!