This item isn't sold by Sears but a third party seller called ErodE, so unlike Sears they most likely don't have the sizing option. However, they also didn't list the size of the dress in the details either. It would be best to contact them, and ask what size the dress is and do they have any others for you to look at.
Email - firstname.lastname@example.org
Phone - 281-410-8820
The item number to this dress is SPM3735217021