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?

The above commenter and others have made the claim that Stallman is just being "precise" and "correct" about a misapplication of what sexual assault means, which is exactly besides the point and a red herring. They have also made the claim that "she would have presented herself as entirely willing". That is also besides the point. A 17 year old is a child, and that should have been enough for Minksy to not have engaged with her like that, and to recognize that Epstein was taking advantage of her (and in fact, trying to take advantage of him by offering her to him). That should have been enough. Making arguments about definitions or that she appeared "willing" are illegitimate attempts to deflect a serious moral failing. That in and of itself is a moral failing of Stallman, compounding Minsky's failing by trying to defend it.