“She’s amazing,” Erin, 35, exclusively told PEOPLE about the 33-year-old McPhee on Saturday at the BLEUSALT Launch Celebration in Malibu. “I really like her. She’s awesome.”
She continued, “My dad is kind of a hopeless romantic, and Katharine’s awesome. We really, really like her, and we’ve known her for a really long time. And if he’s happy, we’re happy.”
Last week, the two were photographed walking arm-in-arm in Brentwood, California. A source told PEOPLE at the time, though, that the pair are platonic and were merely having “some fun” at the expense of photographers.
Erin also squashed further rumors that McPhee would be David’s fifth wife on Saturday. (The legendary music producer has previously been married to B.J. Cook, Rebecca Dyer, Linda Thompson and Yolanda Hadid — from whom his divorce was just finalized.)
Rumors about David and McPhee’s relationship started in September after Erin shared photos of the pair at the Grammy Museum’s third annual gala at The Novo in Los Angeles, writing in the caption, “Excited about my new step mom.”
A source close to the situation told PEOPLE at the time that the social media posts were a joke.
“This is not at all true,” the source said of the dating rumors. “Erin’s quite obviously tongue-in-cheek and sarcastic Instagram comments were pointed at those who can’t seem to grasp that her dad and Kat can be colleagues, collaborators and longtime friends without it being some big romance. They can’t even perform together without people saying they’re headed down the aisle. Erin was messing with people who jump to conclusions.”
McPhee has previously collaborated with the 67-year-old Grammy-winning producer for a few live performances (including his 2008 PBS tribute concert Hit Man: David Foster & Friends).
RELATED VIDEO: Watch: Katharine McPhee Performs Her New Single ‘Lick My Lips’
At the September Grammy event, McPhee spoke about how much Foster means to her.
“He’s an incredible friend and I just pinch myself when I get to spend time with him on a personal level,” the “Lick My Lips” singer told Entertainment Tonight. “I love his outlook on life and how he treats people. He’s a really a special person in my life.”
“What I’ve learned from him is how lucky we are to do what we do,” she added. “He’s always reminding me and it’s comforting to know that it’s possible to walk through this life he’s had — working with incredible people, being friends with ex-presidents and world leaders — and still have that perspective. He’s so well-connected, but still just a simple guy from Canada with his little Canadian accent!”
During the Saturday event, Erin also opened up to PEOPLE about the new TV show she’s developing called Daddy Issues, which was inspired by her own life.
“Originally I was writing this show about two girls who are bad at their job, and it didn’t really make any sense. And [Fox] was like, ‘Is this what you want to be writing, or do you want to write something else?’ I was like, ‘I guess I kind of want to just write about the things that people think are funny in my life, which is having a dad who dates girls my age,’ ” Erin continued.
She added, “It’s like, you write what you know, and this idea came about where if my dad basically started dating my best friend and she became my stepmom, what that would be like. It’s never happened. But it definitely could happen.”