Question

click to correct the pronoun if needed. the mayor of springfield almost single - handedly rescued the local arts museum. it was her who donated the money necessary to offset the museums budget deficit.

Explanation:

In a cleft - sentence structure like "It was... who...", the subject form of the pronoun should be used. "Her" is an object - form pronoun, and the correct form is "she".

Answer:

It was she who donated the money necessary to offset the museum's budget deficit.