GenieSoft has the wonderful (I use it) Overture program, and a nice simplified version called Scorewriter II that costs about $50.00--I hadn't realized that Harmony and Melody Assistant were available in Mac versions--Your friend might end up wanting a big professional program, but I would recommend starting here--

Keep in mind, though, that this is the software that folks use to write notes and chord symbols on a printed page, not programs for creating MIDI's, and not programs for actually recording music--which are music programs, as well.

I mention this because you were a bit unclear as to what your friend's daughter simply want to write music which she will offer online, or whether she wants to create music files that people can listen to and download.