Kathy Hilton joined Real Housewives of Beverly Hills for its 11th season, which premiered in May

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Kathy Hilton has quickly become a fan favorite in her cameos on The Real Housewives of Beverly Hills this season — but her youngest daughter, Nicky Hilton Rothschild, is shutting down the possibility that her mother will reach diamond status and join the cast permanently. 

"I do not think she would," Nicky, 37, tells PEOPLE of her mother while promoting the grand reopening of Serendipity3 on Friday. "I don't think she has time for it. It's a full time job."

PEOPLE confirmed last October that Kathy, 62, would be joining the Bravo franchise in its 11th season, which debuted in May. Kathy appears alongside sister Kyle Richards, who has been a part of the series since its 2010 debut. Kathy and Kyle's other sister, Kim Richards, previously starred on the show's first five seasons.

Nicky Hilton and Kathy Hilton
Credit: Vittorio Zunino Celotto/Getty

Following the news of her mother's casting, both Nicky and her big sister, Paris Hilton, revealed that they weren't exactly thrilled by Kathy's decision. Despite being initially ambivalent about Kathy joining the show, Nicky says that she has been tuning in.

"I am watching," she says. "I [was] absolutely hesitant because I watched the show and I know how drama-filled it is. But I like that she has managed to stay out of it for now. We'll see!"

THE REAL HOUSEWIVES OF BEVERLY HILLS -- "The Divided States of Erika" Episode 1105 -- Pictured: (l-r) Lisa Rinna, Kathy Hilton, Sutton Stracke --
Credit: Nicole Weingart/Bravo

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Nicky is thrilled to see how RHOBH fans have positively responded to Kathy's presence. "It's so funny, I get tagged in memes all day and she barely knows what a meme is. So, I'll send it to her," she continues. "It's pretty hilarious."

Long before they were bonding over RHOBH memes, Nicky and Kathy created cherished memories of visiting Serendipity3, beginning when she was a child. 

The iconic N.Y.C. restaurant (which also sells several ice cream pint flavors, including Cookies & Cream Remix, online) officially opened its doors again on Friday after being closed for over a year due to renovations.

Nicky Hilton
Credit: Craig Barritt/Getty

For Nicky, being a part of Serendipity3's reopening event is a "very heartwarming and nostalgic and special" experience.

"I am a very proud born and bred New Yorker and Serendipity is an institution. I have been coming here my whole life," Nicky, whose favorite item on the menu is the Frrrozen Hot Chocolate, tells PEOPLE "My mom always ordered the foot-long hot dog. Of course, we all have frozen hot chocolate during wintertime."