No. You can book a flight for someone else if you have enough miles tho.
"Mileage credit and award tickets are non-transferable. Mileage credit cannot be transferred from one FREE SPIRIT account to another (other that with respect to duplicate accounts as described in item 27 below). Free Sprit miles cannot be sold, gifted, attached, or seized. FREE SPIRIT accrued mileage credit and award tickets do not constitute property of the member. Neither accrued mileage credit, nor award tickets are transferable by the member (1) as part of a domestic relations matter, (2) upon death, or (3) by otherwise based on the operation of law."