The National Enquirer this month ran pictures that appear to show the teen snorting cocaine.
However, her father told ABC News: "I don't know anything about that. ... My daughter, she doesn't, she doesn't do that."
Bobbi Kristina, whose mother is singer Whitney Houston, insisted via Twitter she was "set up" by an ex-boyfriend following "a horrible relationship that went sour."
"It's really not what it looks like," ABC News said she tweeted.
Brown, a former member of the group New Edition, was married to Houston from 1992 to 2007. The couple endured a stormy relationship during which both battled addictions to drugs that sidelined their careers.