Hello sparkle,
this is one long thread, I've read some of it but not all,
why did you let her continue tiling after day 1? The job can only be described as a mess,
did you not ask to look at some of her work prior to her starting? Not wanting to come across as harsh but that's the 1st thing I be asking before I let someone loose on something that mattered to me,
what ever excuses she's using its pony, rule number 1 for me when pricing a job is check walls for plumb and straightness and floors for level so I can quote for the right amount of materials and the right amount of prep work,
good luck