sorry to post twice, but the troll reference is irresistible.
(tugging with both hands to remove tongue from cheek...)
perhaps she means to claim descent from a member of the Tuatha de Danaan, the
"people of the Goddess Dana," considered (choose your mythological
interpretation) to be pre-Christian inhabitants or gods of Ireland.
They invaded the island and took it away from the equally mythical Fomori
(who had only one eye and lived under the sea, no Atlantis references
please) and the Firbolg (who according to one book I have might have been
real, pre-Goidelic inhabitants). But the Tuatha were in their turn beaten by
the invading Milesians, sons of Milesius or Mil, who were avenging the death
of their cousin Ith.
The Milesians drove the Tuatha literally underground (don't trolls live
underground?), after which they became known as the Aes Sidhe, the people of
the (hollow?) hills.
so, spinning out this extended conceit, your friend may be claiming faery
blood. crack no jokes on her heritage until you lay hands on cold iron.