There is so much information about this case, from various sources it is hard to keep track of what is fact and what is speculation. These are a few questions I'd like answered that I haven't heard any information about yet:
Was her purse/credit cards ATM cards left at the house?
Was there evidence of burglary (stolen items) at the house?
Were her ATM/credit cards used after the event?
There is an expression : If you hear hoof beats, think horses not zebras. So perhaps this case is no different than hundreds of other similar cases with very common motives and actions and people are going down all sorts of paths simply because she is the mother of a famous person.
Here is a theory I have: The person or persons who did this simply saw an easy target (an elderly feeble woman with limited mobility, living in an expensive house, and where there were no neighbors that had a clear view of her house) so they took the opportunity to take what they wanted. And they had no idea she was the mother of a famous person. What they wanted was either: property/money, an SA (it happens even to 84 year olds) or simply for the thrill of it. If the murder did occur in the house, they did not leave the body because bodies can produce a lot of evidence (trace evidence, DNA under the fingernails, projectiles, etc.) so instead they decided to take her and dispose of her somewhere in the wilds of Arizona. I suspect, if she was murdered, that they did not commit it in the house but instead transported her somewhere and then murdered her after they got what they wanted. In many cases like this, the perps want the person to use their ATM card so they force the person to go with them so they can use the card. It could also have been someone she could recognize (a former worker at the house, a previous Uber driver, etc), so the killer had no choice but to murder her even if it was simply a botched burglary.
The ransom notes IMO are either a hoax or, if the killer is very stupid, from the killer to try to get LE to look into the kidnapping/ransom angle.