So Lily's outburst was a bit of an oddity to me at first. She was written as perfect young girl with no flaws besides her blindness. I wasn't really surprised that she got angry so much as I was confused by her reason for being angry. My first and only thought before continuing on was that she was angry that kenji yanked her to the ground by accident. She was born blind, so if I was her and I was suddenly yanked to the ground, I'd be irritated too... remember you didn't see it coming (pun kinda-sorta intended lol).
As for the other ideas posted, it being a foreshadowing of her having to move to Scotland makes a lot of sense.
After having played through Emi, Hanako, and Shizune's routes, Lily's is my favourite by far (Hanako's is second). It was well written, emotional, romantic and very touching... even though I think they over-played Hisao's heart condition too much. The warm-fuzzies I got at the end of the story were good, I was crying, and then I uninstalled the game because I wanted this to be Hisao's final route. xD ...and Rin didn't really interest me.

