Pierzina was voted out by the other houseguests last week, meaning that she was the fifth contestant to leave the show this season.
Chen has now told Entertainment Weekly that she believes Pierzina was "a little bit embarrassed" about the situation.
"She was slightly humiliated that she didn't make it to the jury," she said. "She didn't make it far at all this time, and I think she felt embarrassed that she got played. Up until last night, she helped to invent the game! But the gamer got played."
Chen also praised Pierzina for being "brutally honest" about her rival Boogie, saying: "That's what made viewers fall in love with her from the first season. She owned who she is. She called out the nerd herd to their faces. She doesn't make any excuses for who she is, and everyone loves her honesty."
However, Chen suggested that Boogie - whose real name is Mike Malin - is running the Big Brother house now.
"He is now the puppet master," she said. "He has that entire house on strings. He's not even discreet about it!"
Big Brother airs on CBS.
> Big Brother USA Janelle Pierzina on eviction, Boogie, strategy, more