Sigriðus is an important figure for the myth surrounding the waterfall. She lived all her live in Brattholt, a farm that still exists today. Sigriður and her sisters would often guide the visitors all the way up to the waterfall, they built the first trail that led down to the waterfall. She did not receive any official education but was well read and artistic.
In 1907, landowners including Tómasdóttir's father, Tómas Tómasson, a signed a deal to allow the construction of a hydroelectric dam across the Hvítá River that would result in the submergence of Gulfoss. Upset by the deal, she took legal action against the development. Sigriðus efforts ultimately failed with the legal system but gained positive public attention. The lease contracts later were canceled and the hydroelectric project was never constructed.