You are probably using the wrong search engine.  The best of several available on this site is the "Digitrad and Forum Search", which you will find on the main Forum page.  McKennitt is a popular performer who has been discussed here quite a lot, and lyrics for a number of songs she has recorded have been posted in the Forum, though likely enough few if any have so far made it into the Digital Tradition database.  For more about how the DT and Mudcat work, see the FAQ thread at the top of the threads list on the main Forum page.