Warning: Graphic.
The night before Gannon went missing, SOMETHING happened. I know we're not allowed to reference certain topics. But my theory is she went into a rage and threw something, and glass was broken. Gannon may have been injured by broken glass. Maybe as he tried to run, or during a beating. That could explain the blood in his room. He may have scurried there to escape. I think the charges about knives and guns relate to them finding a decent amount of blood in his room. Not necessarily enough to prove he was dead, but enough to prove he was injured enough to need medical care that he never received. I don't think anyone else directly witnessed whatever happened. So they are covering all bases by adding knife/gun charges to explain that bleeding.
I've always agreed with the theories that she (also) punched him in the abdomen that night or otherwise did internal damage that became more obvious as time went on. By the morning she knew his injuries would be fatal if she didn't seek care immediately. But out of self-preservation she made plans to hide the "accident"
by NOT seeking medical care, just allowing him to die and then ditching his body.
I think she drove around so long because she was waiting for him to die.
Maybe he was slowly dying when she kept looking out the window at the store... and it was taking too long. Soon she'd have to be back home, meeting up with L as she got home from school. Her story that he "went to a friend's house" wouldn't work if she was late. So she took him to the side of a rural road (likely where the later sifting and searching happened) and beat him with the 2x4.
She ditched him and the murder weapon quickly, because she was in a hurry to get back.
Afterward, she realized her Apple watch would give away Gannon's location if cops started viewing her as the main suspect. After finding out on Feb. 2 that the neighbor's video made it obvious she was lying (I speculate she knew about the video before police even did, as AS confronted her right after neighbor showed him -- JMO), she knew police would soon start retracing her movements. But first they'd need to get search warrants. So she immediately went back and removed his body, making sure there was no GPS tracking this time. I think LE weren't actively following/tracking her yet. Soon thereafter, they sure were!
When she moved Gannon, she missed the sock and the board. (ETA: She also likely put him into a suitcase she bought after leaving the family home.) She may have stashed Gannon's body somewhere and moved him to FL later, or she may have headed out to FL right away on Feb. 3rd. I don't think anyone knowingly helped her, though relatives may have helped her lay low and disguise her movements due to all the supposed death threats she was getting. I think LS is 100% accountable for Gannon's death and hiding his body. All just my opinion and speculation.
RIP Gannon