This can be important. When Charlemagne's first son was named "Pepin" -- this is a matter of evidence about his parents' union. Not conclusive. There are arguments to this day about whether they were married, or she was his concubine, or perhaps the union was less regular form of Germanic marriage. But the name in itself was evidence that Charlemagne considered his son to be in line for the throne.
Given that her father was nowhere near -- having repudiated her mother -- and was otherwise childless, naming her outside the common names of her father's line could have been a spiteful gesture on her mother's part, that he threw away his chance at an heiress. Then, spite does not fit her character. . . .
Neither, on the other hand, does arrogance, and that would be naming her daughter as if she were the heiress. She resorted to a name from her own family, I conclude.
And all this for a throw-away sentence in the novel.
