Parents have given some wonderful suggestions about what might be going on - including nothing! I'd like to add, if it continues take her to the pediatrician to check for ear or throat infection, and discuss possible allergies, her diet, possible acid reflux, and possible food sensitivities. If the baby screams for an extended period as if in pain, she really might be in pain. My baby did this and the doctor said it was normal, but she never saw it. When my parents did they were aghast because it was not normal stuff - it was pain. We can tell the difference, I think. If you think it is pain, it probably is. That doesn't mean the pediatrician can easily figure it out. At two she was diagnosed with migraines. Who ever knew a baby or toddler could have migraines!? I sure didn't. But it gets even more complicated because migraines can be from allergies and food sensivities, or from other conditions.
So mostly what I am saying is IF you think this really is screams of pain, get it checked out.