Two different people have been merged here

These parents may have had a daughter named Berthilde, but she surely didn't marry her brother. Dagobert's wife is listed in Wikipedia as Berchildis. Much is made of criticism of Dagobert's many wives, and certainly if one of them had been his sister, something would have been said. People weren't even supposed to marry the sisters of their close relatives' spouses, and a full sister would simply not have been allowed by the church.