Thanks a lot for all your responses. My mother finally traveled on Cathay Pacific flight in the following itinerary. She was worried about the transfer in Singapore. Thanks to AA miles, this was possible.

SFO --> HKG
HKG --> MAA

This flight had a two hour stop over at Honk Kong.

Anyways, here is what I heard from the airlines on the previous itinerary :

United: On the phone mentioned that they can check the baggage all the way to MAA. The agent told that they cannot issue a boarding pass for the flight from SIN to MAA

Air India: On the phone did not provide details on where to get the boarding pass. The AI agent mentioned that my mother has re-checkin the baggage.

Thanks for all your responses.

...mottai