There is no one definitive answer to this question. Depending on who you ask, PDA girl could mean a lot of different things.
Some people might say that PDA girl refers to a girl who is comfortable with public displays of affection (PDA). This could mean that she doesn't mind kissing or holding hands in public, or even engaging in other forms of physical intimacy. Others might interpret it as meaning that she is simply an affectionate person in general, whether that manifests itself in public or private settings.
Still others might use the term PDA girl more colloquially, to refer to a girl who is perceived as being easy to flirt with or sleep with. This usage is often seen as derogatory, and so it's not surprising that many people would be hesitant to self-identify as a PDA girl.
Ultimately, the meaning of PDA girl depends on who you ask and what their personal interpretation is.