She was also convicted of forcing companies to sign lucrative deals with firms owned by Choi and donate gifts to Choi and her daughter.?

deals 應該是指"多筆數的契約"所以是對的.

"deal" is a countable noun when it means "an agreement for buying or doing something" 交易；協議.

"deals" (plural) indicates more than one deal (that she forced companies to sign with firms owned by ....)

Don't be confused with its other meanings (待遇, 特定政策) that are usually in singular form.

假如指控或罪狀是一宗/單一"交易"寫法便是
to sign a lucrative deal

但事件應該是多項不法的行為或交易，前句的companies已指出她是操控多間公司的，後句說出跟Choi的firms亦指出跟多間他擁有的公司(眾數)交易的話，前句的deal便不可能是單項交易，所以是deals.

My amendment of that sentence on question: She was convicted of persuading ABC company to sign contract with Mr. Choi's so as to offer that bribe. Yip