Excited Haylie added, "It's pretty cool to think our daughter is going to be at our wedding."
Haylie Duff and Matt Rosenberg at the Santa's Secret Workshop
The 29-year-old was attending the Santa's Secret Workshop in LA over the weekend, where she also opened up about her pregnancy diet.
"I drink a lot of green smoothies," she revealed. "I think I've craved health food, which is weird, and then the occasional mac and cheese."
Haylie – who is in her second trimester - said her focus is on staying fit, although her workout routine is making dad-to-be Matt a "little nervous".
"He's like, 'Don't push yourself too hard'. I'm like, 'I got it! I'm fine'," she revealed. "I'm just trying to move. Go on walks. I'm not trying to put too much pressure on myself either way.
Haylie and Matt got engaged in April of this year
"I feel better when I'm active. I try to do something every day, even if it's just a little walk or whatever, but there's some days I don't do anything."
Haylie, who is the older sister of Hilary Duff, revealed the news of her pregnancy on her food blog, The Real Girl's Kitchen – and also confirmed the baby's gender.
"Today we have big, exciting, wonderful, magical, amazing news!" she wrote. "Matty and I are expecting a baby girl!
"Entering this new chapter of our lives and our relationship has been so special. We are so happy and so in love with her already!!"