In the episode, she suggested that Wainstein might have an eating disorder – noting the new star's thin frame.
"She looks like a really thin girl ... she looks like there's an issue," Frankel said, adding, "I wrote a book called Natural Thin. This is not natural thin."
Later on Watch What happens Live, a caller asked Frankel about her tendency to give hard times to new Housewives, such as Wainstein.
"We have a little bit of a rocky road. Ultimately we're okay, but listen, they come in and I say what I think. It doesn't matter if you're new or old," Frankel said. "I have ripped Ramona [Singer] and Luann [de Lesseps].
She also summed Wainstein up to Andy Cohen this way: "She's beautiful. And she has a credit card. So there's that."
After WWHL, Frankel tweeted that she holds "people accountable" when asked if she considered herself judgmental.
Yes and no. I hold people accountable. https://t.co/liNPw0eWhH— Bethenny Frankel (@Bethenny) April 7, 2016
On RHONYC, Frankel said part of her concern came because her mother Bernadette had an eating disorder.
"Wainstein reminds me of me mom. It freaks me out a little bit," said Frankel.
The Real Housewives of New York City airs Wednesdays (9 p.m. ET) on Bravo.