Here is another theory:
If Mona was really angry because of a debt with SE, or if this was a drug deal gone wrong with SE, how come she didn't implicate SE?
She picked DD for some reason.
I don't know if it that was because MN was sitting there that day while police were questioning everyone, and how much information she was able to collect off cuff. In my head, the only thing I can think of is that MN was super calculated that weekend. I am pretty sure she passed the roads she traveled before thinking that there were no cameras. I wonder if she knew anyone that worked at Alloy and asked prior "Do your cameras work?" I honestly believe that the cameras on and working that day were a God sent. MN seems too calculated, she scares the chit out of me.
Hmmmm, you know what? This could be where this mysterious plastic container came into play in Q's interview last night. Someone stated this earlier, tied up and put in a container. Maybe Mona is now trying to cover her tracks in blaming DD and the "he gave me a container to get rid of." Still doesn't explain why she was so drunk and went home and did what she did. (**NOT saying she was drunk, that is what MN has said.***)