Cardi B isn't denying that she's a Blood -- just which set she's affiliated with.
Cardi B has, somehow, found herself in the middle of Tekashi 6ix9ine's case. Perhaps, New York City is smaller than the world thinks. Anyways, Cardi B's name was brought up in the middle of his cross-examination when he was asked if he knew that Cardi B was a Blood. He confirmed that he did know that she was blood but the only reason her name was mentioned was that Aljermiah Mack's attorney asked 6ix9ine if he copied Cardi B's template to get famous (i.e. using Bloods in her music videos etc.)
Since then, Cardi's rep denied that she was a member of the Nine Trey Gangsta Bloods. Later on, she seemingly made light out of the situation with two hilarious memes. Eventually, she actually clarified that she is a blood but she's never been a Nine Trey Gangsta Blood, nor has she been affiliated with them. She did reveal that she's associated with the Brim Bloods set. She revealed her affiliation in a since-deleted tweet but XXL managed to capture it.
Cardi was not the only famous rapper mentioned during 6ix9ine's testimony. In fact, there were a few of them mentioned while the rapper took the stand in the past few days. 6ix9ine also mentioned Jim Jones during the trial and revealing that he's a member of the Nine Trey Gangsta Bloods. He has yet to respond to the claims.