Research Notes:
On 9/11/2015 Peter Stewart wrote, "The ancestry of Bertrada is unproven. The suggestion that she was daughter of Theoderic III is based on the inheritance of Rommersheim jointly by Charlemagne's parents. Another theory relates her to the Merovingians only through marriage." [1]
[1] Newsgroup Post, soc.genealogy.medieval, Peter Stewart, 11 September 2015, [GoogleGroups_SGM].