The 60-year-old singer, who has kept a lower profile than most of her relatives, said on US TV's The View: "A day doesn't go by where I don't think about it - think about him. Some times in the middle of the day I just break down and start crying."
Rebbie dismissed reports of dissent among family members over the distribution of Jackson's estate - and insisted the trial over his death has instead brought them closer. "Everybody is working toward wanting to see justice because of the way he died," she said.
"I have faith in the judicial system and we are going to find out the truth with everything in these few weeks."
She also admits that the "family was very much aware" that Michael had problems with drug use and "there were many times there were interventions".
"But even though that's the case, still it has to be explained and exposed what happened at the end," she stressed.
She said her mum Katherine "seems to be holding on", adding: "My mum has a very strong constitution - she knows what she wants to do and she's doing it just fine."