Question

Rewrite the sentence to make the pronoun reference clear.

Sherrie told Sarah that she needed to work on her spelling.

Answer 1

Focus on subject
Sarah was told she needed to work on her spelling.

Answer 2

Not a bad solution, however you do lose a bit of information (that Sherrie was the one who told Sarah)

The typical way this is corrected is just to repeat the desired antecedent

So something like “Sherrie told Sarah that Sarah needed to work on her spelling.” Would also be a viable solution