Ginny surely didn't know Parseltongue. It was a dark and rare skill.
Talking about Riddle's diary, it was merely hypnotizing Ginny.
But, how exactly did Ginny control Basilisk without knowing Parseltongue?
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There's no reason to believe she was physically incapable of producing the sounds; Ron was, despite having no inherent ability to speak the language.
The stickier bit is language comprehension; obviously Ginny had none. Fortunately, her body was being controlled by the fragment of Voldemort's soul. If it was controlling her bodily actions (for example, forcing her to string up Mrs. Norris and paint the walls in chicken blood), there's no reason to believe it couldn't also control her vocal chords.
Finally, we have evidence that being possessed by a piece of Voldemort's soul confers the ability to speak Parseltongue: this is exactly how Harry is able to speak it.