I would argue in both of those sentences you should use the past tense of 'wants', which is wanted. "If she knew what she wanted" she wouldn't have broken up with me. "If she had known what she wanted" she wouldn't have dumped me, only to get back together with me 6 months later. To use it in the present tense, it would be: "If she knows what she wants" ...she will pick me to be her boyfriend.

I am no native speaker, yet I hope I can give you some proper advice. 1) If she knew what she wants >>> Talking about a girl, who, in this very moment, doesn't seem to know what she wants. Notice: Even thought the verb "knew" is a past form, this conditional is used to talk about the unreal PRESENT, like a dream or hope. That's why it's called the "Present Unreal Conditional". ~~ "If she knew what she wants, ....we would get together." 2) If she had known what she wants >>> Talking about a past situation! Notice: We're not talking about some unreal situation in the present, but the past. That's why it's called the "Past Unreal Conditional". ~~ "If she had known what she wants, ....we would have gotten together years ago"