1. She will be treated as an Indian National candidate and her state code of eligibility will be the state she is currently residing.

2. She has to pay the fees as other Indian students pay.

3. Yes of course she is eligible for JEE Main and Advanced.

A paragraph of NTA JEE Main Information Bulletin 2020 says, " The State code of eligibility of OCI/PIO passing Class XII (or equivalent) examination in India is at par with Indian nationals. However, OCI/PIO passing the Class XII (or equivalent) examination from an institution abroad are eligible for Other State quota seats or All India quota seats (but NOT for Home State quota seats) in all NITs, IIEST and Other-CFTIs"