The Grand Ayatollah Khamenei answered a question about performing Qadha Salaats for parents by the daughter instead of the eldest son.

Question: If for any reason, the eldest son is unable to perform Qadha Salaats and fast for parents, and the daughter is willing to perform them herself, or to appoint someone (to perform them) out of her own money; does this mean that the son is free from the responsibility and there is no sin on him?

The Grand Ayatollah Khamenei: According to assumptions made in the question, the son will not be responsible and has no duty in this regard.

Source: khamenei.ir