Jamie Lynn Spears' cousin Alli Sims says the 17-year-old will make a great mom to daughter Maddie.

"I'm sure the baby's beautiful, and I'm so glad everybody's healthy and doing well," Sims told Usmagazine.com at an after-party for Wanted in Los Angeles on Thursday.

"I just wish them all the happiness in the world," she said. "I know they're going to have so much fun."

(See Us' photo gallery of Jamie Lynn Spears' baby bump.)

Sims — who said she is still "great friends" with Britney (who's recording a new album) — added that she plans on sending "something cute.

"I'm sure they're doing great," she told Us. "I know they're just so excited."

Maddie was born Thursday at Mississippi Southwest Regional Medical Center in McComb, Mississippi.

She weighed 7 lbs., 11 ounces.

(Read what an expert had to say about the baby name Maddie.)