Send an email directly to customer service requesting the change, as they have editing rights to change gender. Rumor has it that at one time, early in the life of SLS, members were able to change profile sexes at will, but abuse caused the ability to be removed, so you will not find any user defined options to make the change.

Looking at your profile, it shows you as a couple, so your concern has already been heard and acted upon. Update your partner's stats, add a few pictures to represent her, and enjoy SLS as a couple.