The correct answer is A. Sally can redeem herself by helping at the picnic.
Explanation:
The word "redeem" means to compensate something, for example, a bad action or to get something back through payment. Besides this, this word is a verb, and due to this, it should describe the actions of someone.
In this context, the sentence that uses the word redeem correctly is "Sally can redeem herself by helping at the picnic" because in this case, the word redeem is correctly used as a verb that is attached to the modal verb "can". Also, its meaning fits in the context because it is suggested Sally is trying to compensate for a bad action or a fault, and the way of doing this is helping.
