Unknown male and female could be her parents, but I think they said they did DNA on the parents, if I remember correctly, and I am sure the brother probably did one also, to rule out any male. They arrested Krystal and got DNA from her. So, who could the male and female be? Well, we could say friends were visiting, perhaps a couple, that had to use the restroom during their visit.
Or did PF have help from a male and female that day? I wonder how old this DNA is? Especially since nurse Ratchett did such a thorough clean up of the crime scene. Who else would have been at her condo just before or after her murder? Things that make you go hhhhmmmm.