She will not use the Gimp if it's not easy to download. Whatever is true for the Gimp goes doubly for Gtk. It would be nice to have Gtk as the go-to C toolkit. And this may simply not happen. The callbacks are a pain in the neck.
Graphical contexts are, too.
Some things are defined constants others are literal strings. All the underscores and long macros and casts and huge argument lists make the code look ugly even in the hands of good developers. All of this maybe necessary for some reason. But given the situation, the documentation and support must be better. All too often I'm very tempted to look for another toolkit.