2 here on average. If she is bad then it is no books. She loves her books so the threat works still :)
Liz, just tell her you get two books at night and let her pick. If she throws a fit then tell her no books tomorrow and stick to it. She will fall in line eventually, but you have to lay the law down.
this is just like emily! it takes a LOT for me to take away her nighttime stories, but when she loses them, it REALLY hits home and she talks about it the entire next day. very effective punishment here! :)