Indeed, obviously she has quite the talent for markdown. Perhaps you could enroll her in some training for web development? She already types better than some developers I’ve met through the years…

Your guinea pig taught you something today.

I don’t typeset music myself but I’ve heard that LilyPond is very good. It is based on LaTeX.

I use Liberapay and have been pretty happy with it. Have found quite a few of the people and projects to which I would like to donate, but not all.

I use Runbox, and have for many years. Overall I’ve been happy with them. I think they have the features you are looking for.