I saw this too and I am on Lily's side. She only has a certain amount of time to get changed and be ready to walk and the dresser asked the same question 3 times (Lily answered swiftly each time then shouted it) and the answer was pretty obvious anyway.
If Lily is late SHE gets in trouble, not the dresser.
My point is, if she is rude in countless interactions then yes, she is rude but I certainly don't think it's fair to judge her solely on that one thing.
Imagine how YOU would behave in that situation before you judge her.