Because the reason she is doing all of that is because she has low self esteem, and wants to flirt with guys for attention so she feels desired, appreciated, powerful, and loved.
When you do the same thing back to her and put the ball in her court and say "sweetie your not even that cute i was just trying to be nice", it deflates her entire self esteem back down and basically just cancelled out and wasted all of those times she spent flirting with you and playing you (which she deserves 100%, i might add).
So thats why she reacts with such hostility, it really bothers her and pisses her off that you would say that. Girls with low self esteem who do this also tend to be selfish... they tend to be unintelligent, not with God, not happy, and dont really know how to succeed in life (hence, why they have low self esteem in the first place). So yeah, they are going to tend to be selfish and hypocritical about alot of stuff. Thats just life
Remember, kids: The less you care about a b*tch, the more shes gonna care about you. Especially girls like this. Girls are so used to getting the majority of guys approval (80% or so of guys, who are the classified "undatable losers"), that when a guy comes along who DOESNT seem fazed or interested in her, while still being cool and popular and getting to know all her friends (the top 15% or so, the cool alpha males)... this drives girls crazy! They want to get to know him and they want his approval and they want him inside her. They crave his validation so bad its like a drug. Learn how to play girls n*ggaa and stop gettin played