My guess is little RJ was sound asleep, but they should still have a qualified person interview him.
It sounds as if either the AC guy or GF's brother/nephews were the last to be able to verify if she was alive and present in the home around 5:45 pm.
I am thinking if she were smoking a bit of pot, LE already knows this information.
If someone was there, I believe he would have been seeing her and this is why should would be afraid to mention it. She knows how her bf would take that piece of news on top of everything else. She is so immature and not so much on the intelligent side which is a bad combination for making good choices right now, imo. Lying about ANYTHING right now is a very bad decision.