Hindsight is a wonderful thing and I'm sure your friend would have gone via another hub if she could or new of the issues at Mumbai. BOM is a nightmare when transferring from domestic to international and I would definitely recommend the international transfer bus over the taxi option. They are attempting to resolve this issue by building a new terminal.

It is fog season in Bangalore and I would suspect this is the reason the flight was diverted.

To be honest I generally take the BA non stop service to BLR and then return via DXB in the evening using emirates/BA. this allows u to get a full day in the office on Friday.