On Saturday, Dec. 21, the actress, 54, and reality star Adrienne Maloof co-hosted a holiday bash and toy drive for Children's Hospital Los Angeles, where she took a brief break from the festivities to open up about her relationship with costar Kardashian, 44.
Chatting with PEOPLE at the party, which was held at The Maloof Estate in Beverly Hills, Nash-Betts said that Kardashian -- her costar in Ryan Murphy's upcoming legal drama All's Fair -- is "lovely."
"I love her so much," the star told PEOPLE, adding that the Kardashians star "really is a girls' girl."
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Nash-Betts also said she loves that she went into filming the Hulu drama, which also stars Glenn Close, "having little knowledge of [Kardashian] personally."
"It was so funny," the actress recalled, "because when we first met, I met her and her mom [Kris Jenner], and I said, 'I have to be honest and tell you, I've never seen your show.' And her mother said, 'Oh, thank God. We have a chance! Maybe you'll like us.' "
Naturally, the trio "just all started laughing," Nash-Betts said. "So I was very unbiased. I didn't know anything about their family."
Regardless of her knowledge level, however, the Grotesquerie star will not stand for any bad-mouthing when it comes the SKIMS founder. "But let me tell you something: You can't say nothing bad about Kim to me," she told PEOPLE. "I will fight you in the street!"
"Don't you say nothing about Kimmy Kim to me," she added, with one final warning: "Don't do it."
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Kardashian recently earned critical acclaim for her portrayal of Siobhan Walsh -- the publicist to actress Anna Victoria Alcott (Emma Roberts) -- on season 12 of Murphy's American Horror Story, which also marked her biggest acting role to date.
Now, she is set to play a successful L.A. divorce lawyer working at an all-female law firm alongside Close, 77, and Nash-Betts -- who has starred in several Murphy projects -- in All's Fair, Deadline reported in September.
And though not much else is known, at least plot-wise, about the drama series, Nash-Betts has been serving up some behind-the-scenes content -- including a photo of herself, Kardashian and Close rocking comfortable PJs together.
In October, the Scream Queens alum shared a picture of all three actresses wearing Kardashian's SKIMS pajamas in an Instagram post, which she captioned, "This is what happens when our leading lady @kimkardashian gifts our cast @skims."
"It's a Pajama Party 🎉 on the set of #All'sFair with the icon @glennclose ❤️," she continued. "Thank you Kimberly 💋."
More recently, Nash-Betts shared footage of a cute behind-the-scenes interaction between herself and Kardashian.
In a Dec. 6 Facebook video, Nash-Betts started singing in what appears to be her on-set trailer before Kardashian said something to her off-screen.
"What did you say, Kim Kardashian?" the actress said, as her costar replied from off-screen: "Good luck tomorrow, Niecy!"