The former treasurer of what had been one of the country’s largest privately held mortgage lenders pleaded guilty Thursday to a nearly $2 billion fraud conspiracy that authorities say contributed to the failure of her employer as well as an Alabama-based bank. Desiree Brown, 45, of Hernando, Fla., faces up to 30 years when she is sentenced in June. She was an executive at Ocala, Fla.-based Taylor, Bean & Whitaker, which filed for bankruptcy in 2009.