Yes, that is what we have seen in other trials. Make them take the stand and make them pick and choose which questions they can answer and which ones they refuse to answer by taking the 5th.
That way it becomes obvious to the jury when they keep saying "i dont remember" to all the other questions, it can imply they are lying for the defendent. And the jury picks up on that.
I don't believe PF's mother was involved in any way with the murder. I think the question everyone wants answered pertains to the alleged fire on her property and whether KK was there. In fact, the DA may give her immunity in exchange for her testimony because LE DID find remnants of a fire. If there was no burn permit, as property owner, she could be facing legal consequences. I think Colorado takes open burning pretty seriously.
JMO