Rosemary DeCristoforo (defendant) opened two credit-card accounts with Citibank South Dakota, N.A. (Citibank) (plaintiff). DeCristoforo used the credit cards to purchase goods and services and to obtain cash advances. Citibank periodically sent billing statements to DeCristoforo. However, DeCristoforo failed to pay the amounts due on either account. Citibank sent DeCristoforo monthly statements advising her that she was being charged interest on all unpaid amounts she owed. The annual interest rate charged by Citibank for these overdue amounts were allowed under South Dakota law and ranged from 10.65 percent to over 50 percent. Subsequently, Citibank filed an action against DeCristoforo to recover the amounts she owed. DeCristoforo filed a counterclaim, alleging that Citibank had violated federal law by charging her interest in an amount greater than 7 percent, which was in violation of 12 U.S.C. § 85 (Section 85). DeCristoforo moved for partial summary judgment, and Citibank cross-moved for summary judgment.