Actually what happened w the mixed DNA could be this:AK DNA (not blood) was already on the floor pre murder, it is common to leave DNA in your own home. During the murder, a droplet of MK blood happened to fall on that profile of AK DNA. It could also have been the case there was mixed MK and other roommate DNA (not blood) all over the place but the prosecution did not test all over.
I could see this scenario, Ak walked around barefoot, left that print at some point in F's room. After the murder, RG was leaving, perhaps his hand was bleeding, maybe he had a dripping knifes etc. That drop of blood fell on top of AK's profile. AK's profile could have been all over those floors so any droplet of blood would have ended up somewhere on her DNA creating the mixed profile
So any of these scenarios, either AK DNA was pre murder and the above happened OR AK w wet foot stepped in dried blood.