Rachel Bilson on the 'Christmas Miracle' of Adopting a Shelter Dog for Her Daughter for the Holidays (Exclusive)

The actress and her daughter Briar Rose are proud owners of a 3-year-old Shih-Tzu mix named Gertie

Rachel Bilson once made her daughter's Christmas wishes come true with the addition of a furry new friend.

The actress, 42, who recently partnered with Rachael Ray’s Nutrish to help give back to shelter animals in Los Angeles, opens up to PEOPLE exclusively about the story behind adopting her now-3-year-old shelter dog, Gertie, for daughter Briar Rose, 9.

"It was Christmastime and all my daughter wanted was a dog for Christmas," Bilson says. "And it was one of those kismet fate things that we were able to get [Gertie], because she wanted a small dog, and sometimes those are harder to come by."

"This family couldn't take her, so I literally picked her up on Christmas Eve and it was a Christmas miracle," adds The O.C. alum. "So we were very lucky."

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Gertie, Bilson tells PEOPLE, is a Shih-Tzu mix with a very particular personality.

"She's very opinionated," the star says with a laugh. "I appreciate how opinionated she is. She stands up for what she believes in, and I think that's setting a good example."

Despite being of a small stature, Bilson adds that Gertie doesn't let her tiny size stop her from "anything."

"She's eight pounds, but she thinks she's, like, 70 pounds and could just stand up for herself against anything," the Welcome to the OC, Bitches! podcast host says.

According to Bilson, life with Gertie also couldn't be going any better, though she and her daughter did recently forget to mark a special occasion in the pup's life.

"I just realized this morning, my daughter and I looked at each other, and we were like, 'We missed Gertie's birthday,' " she says. "And we couldn't believe it because her birthday is so close to my daughter's."

"We were so wrapped up in my daughter's birthday ... and we felt so bad," she continues. "So we're going to get her a little doggy cake and we're going to make it up to her."

Bilson adds: "It's like you have kids, your brain just stops fully functioning."

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Bilson's love of animals also extends beyond that of her own. The star gave back this week at Pasadena Humane, an animal shelter in California, which she tells PEOPLE she is "such a fan of." (Together, they were able to donate 30,000 lbs. of food and $10,000 to pets in need.)

"I think they do such great work," Bilson says. "It was just so great to come together and help such a great organization with Nutrish, and just bring attention to all of these animals that do need homes and other things such as medical attention."

Bilson also notes that Gertie herself is a fan of treats from Nutrish, which were handed out to many of the animals at the shelter.

"She loves the treats," the proud dog mom details. "The treats, you can't go wrong. Let me tell you. The pickiest eaters will eat the treats."

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