Yes and no! If she is not sure of what the job entails and isn't sure if it is the right career choice - its not a bad thing to do one of these cheap diplomas. They are usually written with the very basics - what the job is about, how to apply to airlines, what the interview is like, a day in the life etc etc. It is nothing like what you would learn on a airline initial training course (I have researched this a lot as an instructor/consultant and attendee of many initial training courses for airlines in the UK, Middle East and Europe). However if she is sure she wants to work as cabin crew or in airline operations, she can do a year/2 year course at a local further education college which will give her a proper qualification like a City and Guilds or BTEC diploma. Other than that I would say, if she is 18 and meets the requirements of the airlines, she should just keep applying until she gets the job! And even if you have a diploma/BTEC whatever, you will still have to complete the whole airline initial training course... So, really it is a choice but not a necessity!