The 28-year-old shoe designer -- who is also mom to two boys, 3-year-old Camden and 19-month-old Jaxon -- welcomed her daughter
, Saylor James, on Nov. 23. Tragedy struck just four days later -- her older brother, Michael Cavallari, went missing on Nov. 27 and was found dead in Grand County, Utah, on Dec. 10. Officials reported his cause of death
as prolonged exposure to the elements.