Perry, who was a friend of Brown's mother Whitney Houston, said he wrote a part specifically for her on the show, in the hopes that it would help her cope with Houston's death.
The Good Deeds director told ET that he wrote Brown only a handful of lines, uncertain whether she had the acting chops to pull off her cameo role.
However, he said he was floored by the 19-year-old's performance on the first day of filming.
"I'm so proud of her because she said she wanted to act and I had a feeling she could but I wasn't sure until she hit the set," he recalled.
"The first couple of shows she did, she had very few lines because I wasn't sure what I was getting myself into, but the kid showed up and blew my mind."
Perry recently denied rumours that Brown stormed off the set of For Better or Worse, pleading with the media to leave her alone.
He wrote: "Please leave this baby alone! And she is a baby! Please stop the lies and give this child some room to breathe and grieve."
Season two of For Better or Worse airs this fall on BET.