What about Suzanne Balderstone’s books? I use those for beginners, they’re great as long as you go slowly and explain everything to the student because they have a lot of information. They’re better than harp olympics for young students with no background. There’s a theory one and one with music for playing.
I was trained from the start with Stephanie’s Student Harpist series with my first teacher, and then about a year later I switched teachers to Stephanie herself. She is one of the most amazing teachers I have ever seen or heard of in my life and her Student Harpist series was the best foundation I can imagine. I haven’t actually worked with her Primer set but I don’t doubt that it is equally as commendable. I wouldn’t think that usually an “alternate notation” would be detremental at all – it just may be a way for younger children to be able to read music without having to learn the relatively complicated standard notation. For learning the standard notation – I imagine that Stephanie made her books in a way that “real” music could be easily learned, so it may just be a matter of introducing new notation (like learning a new technique + notation like pdlt or such) and phasing out old notation. For example – how often do you find fingerings placed in “real” non beginner music? Almost never unless using a certain finger has benefits of some manner. Also, in Stephanie’s Student Harpist series, she used a pair of glasses to denote “look!” which meant that there was something unexpected under it; for example: in her piece solace there is a measure with a single G root-5-8