How long does it go on? Mine has a birdy tantrum once or twice a day and so does my budgie -- sometimes the budgie has three! -- and I just figure they're dusting off their pipes. Theirs can last for a few seconds to a minute or two (I think -- it FEELS like longer, though!

). I thought it must be some instinct and maybe it helps their lungs or regulates their blood pressure. Or maybe they just like to hear their own heads rattle.

If it goes on and on, though, there could be something wrong with your birdy.
It could be a cry for attention. What does it sound like? Quakers have this very loud sort of CAW sound that's their flock call. They want to hear from the other members of the flock to make sure everyone's accounted for and OK. Have you tried just popping your head into the room and speaking to your bird when she does that? If she's flock calling, she'll settle down once she hears from you.
How much attention does she get? Clyde is spoiled rotten and if I come home and don't immediately pick him up, he has a loud, complaining squawk that means, "I'M OVER HERE!!!!"

He starts with "hello." Then "hello" gets louder and louder and finally turns into SQUAWK! until somebody opens his cage.
Maybe Baby just wants to be with you!