Easy, I don't think work experience as Cabin Crew will ever be available.. too many regulations regarding training and age.
However, I quite regularly see work experience people around the offices at BA, generally in the management, operations, crewing side of the job. Indeed, the impression I get is that they can actually put together a good package, giving you time around many different departments, including check-in and dispatch as well. Seems like great experience, and would give an inside view of what makes an airline tick.
I'm assuming that you're still at school (forgive me if I'm wrong) so perhaps your best point of contact will be through your Careers Officer. However, I would also give your Aunt a call, I'm sure she could find the time before a trip to have a chat in some of the departments, and see if anything is available, maybe even get a contact for you.
Good luck,
£6