Staff travel tickets are supposed to get the last seat available, which often is a business class seat. That said, the airline and its agents (ground or flight crew) can reseat such passengers anytime if required. Your mother got the seat she paid for, so not much can be done there. No basis for a complaint. AI is famous for shunting revenue pax to accomodate staff travel, so this is actually a report where AI did the right thing .... @:-) See what happened to [MENTION=219623]unicon[/MENTION] here: http://www.flyertalk.com/forum/india...graded-ai.html
... and you will understand why you will not get much sympathy here.