1) weapons—including firearms, firearm parts and ammunition—are not permitted in carry-on bags.
2) gun would be confiscated
3) you have not mentioned whether your sister had any license to carry the gun or not
4) your sister would be charged under section 25, 27 of arms act
5) it i punishable with imprisonment for not less than 3 years and with fine
6) contact a local lawyer and apply for bail