All I can find on Ponislava are numerous internet genealogies listing her as the wife of Neklan and mother of Hostivit. I take that back - I found a book Tabularium Stemmatographicum, Seu Genealogicae Tabulae Regni Bohemiae: 10 : Decadis II. Libri II, Typis Georgij Labaun, 1687 but of course it also doesn't have a source. After all the wife of a legend is most likely one herself. That Ponislava is Unknown-155560. How this one got attached to Slavibor is a mystery.
That raises the question what to do with the mythical Přemyslids. They do have the Questionable template, but many also have the EuroAristo template and some are Project Protected, a few even have the Czech Roots template. My preference would be to replace all but the Questionable template with Category:Legends. I can write an explanation for the bios and propose the merges of the duplicates presently around.