Jessica Simpson and her fiancé Eric Johnson welcomed their first child Maxwell Drew on May 1.
Ashlee Simpson has now revealed that she is "so proud" of her sister, according to Us Weekly.
"There were small things here and there [I advised her on] that you ask your friends and other mothers [about], but other than that, she's great," she said.
However, Ashlee joked that her niece is "definitely spoiled", saying: "You should see her closet! I'm like, 'God, I wish I had your closet!' Her closet is beautiful."
Jessica Simpson was recently named the new spokesperson for Weight Watchers and has vowed to lose her baby weight responsibly.