As someone who's been involved in Cabin Crew recruitment for a number of years, I can honestly say that it's the whole package that matters to an employer, with a good personality at the top of the list of requirements. A good appearance is also important, however, I'm sure any airline will know you don't have to be a size 10 to look professional in a uniform.
If you have nice hair and make-up and you're dressed appropriately you'll stand just as good a chance at an interview as the next person.
The airline I work for has quite a few Cabin Crew who were recruited at a size 16 and provided they don't put on weight (to the extent that we felt it was affecting their health or their ability to carry out their duties safely) then we don't see any problem.
Good luck with your career.
