The 18-year-old got "WH" surrounded by four little birds inked on the inside of her right wrist, reported New York Daily News.
"The doves have a spiritual connotation, flying free I suppose," said Inksomnia owner Mike Cummings who tattooed her.
Kristina went to the tattoo parlor in Alpharetta, Georgia with Nick Gordon, her adoptive brother who now becomes her boyfriend. He got the same tattoo on his wrist to match hers.
"Happy Birthday Mom You will be forever missed," he tweeted.
Kristina wrote, "Now your truly ALWAYS with us mommy we love you @nickdgordon always&forever. (sic)"
The two were accompanied by a group of film crew for the filming of their reality TV show "The Houston Chronicles" that is due to debut next year in Lifetime.
"They were happy at times, and sad at others. When you would talk about their mom, they got sad, but we tried to keep their spirits up," Cummings said.
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Whitney was found dead in a bathtub of a Beverly Hills hotel on February 11.
"Haven't been tweeting much today, I'm sowwy. I'm REALLY REALLY missing my mommy today. 2morrow is MOMMYSBDAY of course (sic)," Kristina tweeted Wednesday.
"Once it hits 12 am mommy it's your birthday & I am going to celebrate it to the fullest!. Bc YOU deserve... YOU deserve Nothing but the BEST! (sic)"