Sigrid the Haughty, Gunhilda, Sigrid Storråda, Świętosława, (967 - 1014) was the daughter of mythical Burislav (almost certainly Mieszko I of Poland and Dubrawka). The medieval chroniclers generally confirm the assumption that her father was Mieszko I, but saga authors (most important of which is Snorri Sturluson) put her father as Skogul Toste.
Her Slavic name is generally agreed as Świętosława, but only as a reconstruction based on a single mention that her daughter was "Santslaue soror CNVTI regis nostri" from the "Liber vitae of the New Minster and Hyde Abbey Winchester" and assumption, that the earlier mentioned daughter would be called after her mother.
External link
site devoted to Sigrid (http://hum.amu.edu.pl/~bkpan/SIGRID/sigrid.htm)