Which personal pronoun correctly completes the sentence? Sheila likes to bake with ...

a. She

b. Her

c. Hers

Sheila likes to bake with her

- this is the correct completed sentence; so we need answer b.

A is not an object, but a subject and "with" needs a object.

Hers is a form of possessive used without the corresponding noun, so we could say " a friend of hers" rather than a "a friend of Sheila".