Brown, 22, died on Sunday. She had been in a coma since being found face down and unresponsive in a bath at her home on 31 January.
She was the only daughter of American singers Whitney Houston and Bobby Brown and had performed as a singer herself.
Houston was found dead in a hotel bath in Los Angeles in 2012.
Brown was found by her partner, Nick Gordon, in the bathroom of their home in Atlanta.
A police report described her death as a “drowning” although it is unclear what led to it.
Bruising was found on the front of her body at the time. Authorities later said she had sustained injuries in a car crash several days earlier, saying they were not the result of foul play.
A photo released by the family of Houston with Bobbi Kristina as a baby
Fulton County Medical Examiner’s Office said the time that had elapsed from when she was found in January will “complicate” its effort to reconstruct events.
It said the initial portion of the post-mortem had been completed and there were no signs of “an obvious underlying cause of death”, no significant injuries and no previously unknown medical conditions.
The cause of death would not be announced until all tests have been conducted, it added, saying that could take “several weeks”.
A spokeswoman for Brown’s family said she died on Sunday surrounded by her family and was “finally at peace in the arms of God”.
Singer Dionne Warwick, Whitney Houston’s cousin, described Bobbi Kristina as “a sweetheart”.
“She will be missed, that’s for sure. She was a good girl. She was a good little girl. She really was,” she told the Bravo TV network.
The BBC’s Regan Morris in Los Angeles says Brown had dreamed of carrying on her mother’s legacy as a singer and actress, and had a few small TV roles – but her career had not yet taken off.
The day before she was found in the bath, Brown had tweeted: “Let’s start this career up&&moving OUT to TO YOU ALLLL quick shall we !?!???!”
She began performing with her mother as early as 1999, singing duets of My Love is Your Love and recording Little Drummer Boy for a holiday album in 2003.