Self injury is often not a type of parasuicidal behavior. It’s a coping mechanism. However, if the girl has very superficial wounds and is showing them to other people while smiling, I would consider either embarrassment (per the smile, not the showing), or attention seeking behavior. Likewise, the evidence of only 3-4 cuts suggests that she is new to the practice, and having exposed the superficial injury to a peer in a mixed setting would point to her seeking attention.
Self injury when used a coping mechanism (which is most often the case), is a very complex issue. There are a multitude of reasons why an individual (often women), do so, and while this girl may be the exception, rarely is it done for attention or as a feigned suicide attempt.
I would like to suggest though, that while this may be for attention, her actions reflect that she is disturbed. Anyone who seeks to harm themselves for validation have issues that should be addressed by a qualified therapist.
Either way, this should be reported to the teacher/school counselor. They will address the situation from there.