Before she know me or before she knew me?
Certainly, "she know" is wrong.
I expect "Before she knew me..." is correct for what you have in mind, but there are situations in which you could have the phrase "before she knows me" as the correct one.
Can you write the full sentence?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.