That's great you have scheduled a vet visit - that should be the first thing to do, ie. rule out any physical problem.
I'd like to know more if that is ok. Is she really eating absolutely nothing or is she eating very little? Does she get fresh veggies too? Are you able to weigh her and see if she is maintaining her weight? How old is she? How long has she lived with you? Is she showing signs of hormonal/nesty behaviour? You said she has done this before - can you remember when that was? This time last year? What happened last time that she stopped screaming? Where is her cage situated? By a window? Wondering if she can see something or hear something? Have you tried turning on the radio or having some background music/talking? Behaviourwise, can you notice what happens immediately before she starts screaming (the cue)? And what happens immediately afterwards (the reinforcing consequence) eg. attention from you, etc? What is she doing when she is not screaming? What are you doing then?
She is eating very little, but she seems dissatisfied with all foods. Like she will take 1-2 nibbles and then walk away screaming as if something is wrong with the food. I thought maybe it was stale or something so I opened up new bags of her pellets and seeds, but she turned her nose up at those too. I monitor her weight every day, she has lost ~15g over the past month but is thankfully still at a healthy weight (confirmed with the vet). She is 2 years old and has lived with me for pretty much her entire life, about 1.5 years. She is very hormonal/nesty, she keeps doing mating dances so I assume that this behavior is at least in part related to hormones, but she was given a lupron injection at the vet about 2 weeks ago and it did not improve any of these behaviors (she has gotten a shot once before and it stopped her nesting behavior, this time it did not). I assume that the screaming is in part related to hormones because last time that she did the whole "constant screaming" thing was a similar time last year. That time she just stopped on her own suddenly and with no notable cause. This time it has lasted longer and been more excessive, and given the fact that she has already had a lupron injection I am confused on what else I can do. I of course am continuing her with decreased daylight hours, mixing up her cage and environment, not petting her below the head, and providing a variety of food options, but nothing is working.
Her cage is not situated by a window but she likes to hang out near windows, but I have been keeping the curtains closed for fear that opening them might increase the hormonal behavior. She can absolutely hear the outside birds which has been my leading theory for the screaming for a while, but there is no way to fix that of course. I have tried playing music and talking, but it either makes no difference or makes the problem worse depending on the day.
Behaviorwise there is no indication of any cue to the screaming, she just starts from the second that her cage is uncovererd and continues throughout the day. I have tried a number of responses immediately afterwards, none of them rewarding (I do not give her attention for screaming, do not yell at her to stop, etc. I just sit there not looking at her and keep a completely disinterested expression, but that achieves nothing). I have attempted putting her away when she is screaming for brief time-outs, but that does not achieve anything either. She is honestly never not screaming; she will scream while eating, while playing with toys, while getting (above the neck) snuggles, even while falling asleep. She screams when I am with her as well as when I am away (in fact she tends to be more quiet when I am away, hinting to me that she is likely trying to ask me for something by screaming, but I don't know
what).