I don't know who CJ Cherryh is, but her view is incorrect.
Gaelic Languages inflect the prefix for case, so your example of "thee na shee" would likely mean something like "of Daione Sidhe." DEE-nah SHEE is the nominative.
The spelling to incorporate what you suggest would be "Dhaione Sidhe." (note the 'h')
Fact remains, only Erse and Scots Gaelic can win the prize for obscure spellings of beautiful words
.