It does seem entirely possible (not sure about ‘most plausible’) she would have presented herself as entirely willing. I see no fundamental problem with that statement. (Note that there’s a huge difference between ‘presented herself as entirely willing’ and ‘was entirely willing’, which I should hope you’re keeping in mind.)
Legally, a 17 year old may be a child in many jurisdictions, but that fact alone has little bearing on their appearance and maturity, so how is it relevant to the topic here? Had she been several months older at the time, would that have had any bearing on her interactions with Minsky, given her situation?