Hi Eliza,
There are a few good collections in that list but also some to possibly avoid, such as the Bunting Collection (she would have to edit the piano arrangements drastically for harp). Star Edwards’ “Easy Celtic Solos” are indeed easy but the arrangements are not traditional if one cares about such things.
I think that for a good introduction to paying Celtic styles it is very important to listen to recordings and not rely on scores entirely, as accent is often not what a classical harpist might expect. Also, while it varies by region, as a generality Celtic arrangements are sparse – typically open chords and fifths – but with a great deal of ornamentation and you won’t get that just from a score.
Two collections I’d suggest would be those by Kim Robertson and Laurie Riley. Laurie also has published a DVD devoted specifically to that style of playing. Some excellent CDs to “taste” are Alan Stivell’s “Renaissance” and Chris Caswell’s “Holy Wood”. These are wire strung harps from which much (but not all) of so-called “Celtic” music has evolved.
The Carolan collection is great but she should be aware that we only have his melodies so arrangements are by modern players (and not necessarily “traditional” either); Carolan also introduced Baroque elements to the more sparse Irish style.
Biagio