If you want her to start thinking about conservatism as a political philosophy per se, while it's probably too early to start her off with God and Man at Yale, there are several books that, while challenging to a person her age, might be within reach, such as Bias, or if you want more historical texts, have her READ the Constitution, then DISCUSS it. Have her READ the Federalist Papers, or Common Sense, etc...those are most definitely at a high school level.