What is the antecedent of the pronoun in the parentheses?

According to the police officer’s testimony, someone was seen entering the bank just before the robbery carrying a red pocketbook under (her, their) arm.]]> Is the antecedent singular or plural?

According to the police officer’s testimony, someone was seen entering the bank just before the robbery carrying a red pocketbook under (her, their) arm.]]> According to the police officer's testimony, someone was seen entering the bank just before the robbery carrying a red pocketbook under her arm. Type the correct pronoun in the parentheses into the box, then submit it and say the sentence.

According to the police officer’s testimony, someone was seen entering the bank just before the robbery carrying a red pocketbook under (her, their) arm.]]>