It seems generally agreed that Eberhard of Friaul (Friuli) did have a
daughter named Ingeltrud. Opinion is divided on whether or not she
was the wife of Heinrich (maternal grandfather of the German king
Heinrich I), and there are good scholars on both sides of the issue.
The marriage is evidently accepted as valid by K. S. B. Keats-Rohan,
who discussed the matter briefly in "Poppa of Bayeux and her Family",
TAG 72 (1997), 187-204 (see pp. 201-2), with citations to the
literature. On the other side, see the discussion in Werner's "Die
Nachkommen Karls des Grossen (1. bis 8. Generation)", in Braunfels,
ed., "Karl der Große. Lebenswerk und Nachleben" (4 vols., Dusseldorf,
1965-7), vol. 4, p. 452.
So, the "Right answer" appears to be a matter of opinion. I have not
looked at this specific problem closely enough yet to add my opinion
to the others.
Stewart Baldwin