so I presume you ended up agreeing with her that an internship is a better place for getting the mentorship she's looking for?

I say that not to be a dick, or to cause gratuitous offense, but that sometimes, even as adults, we are wrong, and should admit it.

While mentorship programs can exist, and there's nothing stopping them using a open source project as a target, in concept open source and mentoring are not really related.

Both overlap as an "altruistic social good", but the kinds of people who delight in teaching and mentoring and the kinds who delight in writing code (as a way of avoiding social interaction?) would not seem to be a natural overlap.

The vast majority of open-source programmers are doing it for fun (not money) so in their spare time. They probably want to spend that time programming not mentoring. The few doing it as a paid gig, well, they have work to do.

This might just be one of those things that seems like a good fit, but really isn't.