Budgie Crying?

Hi, Two days ago my Budgie started crying non stop and I do not know why, she eats and drinks fine and plays with her toys but still cry's? I have had her for two years and do not know much about her as I found her in my garden 3 years ago, I keep her in a large parrot cage so she can fly around okay. I have other birds, rescue cockatiel ( own cage ) two Red Rumps ( own cage ) to which laid eggs after 3 months of having them and hatched two, now a year old ( own cage ) all my other birds are fine. my Budgie however just wont stop crying and raising her shoulders, any ideas please?