The singer has spoken publicly for the first time to wish Jessica and her new fiance - NFL player Eric Johnson - the best, saying she can't wait for them to tie the knot.
She told People.com: "He's wonderful. They're so easygoing together. They really bring out the best in each other. It's beautiful. I'm beyond excited.
"Right now we're just really enjoying the engagement and their happiness."
Eric, 31, proposed to Jessica after six months of dating, presenting her with a ruby-and-diamond engagement ring.
The first of her family to offer congratulations was her father, Joe, who tweeted: "So very happy for Jess and Eric. May they have a lifetime of joy and happiness."
Meanwhile 26-year-old Ashlee - who is married to rocker Pete Wentz - is also excited about a family party for their son, Bronx Mowgli's, second birthday, this Saturday (20.11.10).
She added: "We're going to have a get together at my mom's, so it'll be fun. He's so sweet, he's very sweet natured.
"He's really into Thomas the Train, and now he's watching movies sometimes."
