In the original rendition, she urinates into the Vímur River, one of the largest and oldest rivers, still around from the creation era. She urinates in it, causing it to overflow, because she's a giantess. Thor, of course, is half giant, so he picks up a boulder and slings it with such force and precision that it hits her 'at the source' and kills her.
Artistic licensing is certainly at play here, and period blood doesn't flow fast enough to overflow a river. Unless she sneezes, but that wasn't mentioned. So. Pee.
Low class, low brow, and, yet, she was one of the nine mothers of Heimdallr. But, Heimdallr fathered the classes, and now we know why. He had some really classy moms, and some really uncouth moms that you'd see on Jerry Springer.
And now we know, and knowing is fifty percent of the battle (the other half is twenty-five percent red lasers, and twenty-five percent blue lasers).