Definition of "Bertha"

You are the beautiful Bertha, the spinner, the queen of Helvetia; / She whose story I read at a stall in the streets of Southampton

1858, Henry Wadswoth Longfellow, The Courtship of Miles Standish

Why couldn't they have called her by her first name, Bertha, which was beautiful and dignified, instead of that silly "Rilla"?

1921, Lucy Maud Montgomery, Rilla of Ingleside, Echo Library, published 2006, page 12

"No wonder she never gets anywhere with a name like Bertha," Sally said, while having coffee afterwards with two of the other night-coursers. "It goes with her outfits, though." ( Bertha sports the macrame look, with health-food sandals and hand-weave skirts that don't do a thing for her square figure, [...])

1983, Margaret Atwood, Bluebeard's Egg, McCleland-Bantam, page 135