I just wanted to add some current thoughts:
Is this an immune-mediated problem? We are not sure -- because we are not seeing any improvement with the drug therapy but in some cases you don't. So wondering about trying other drugs -- vincristine shot(s) again?
Could there be bleeding somewhere else in the body. We did have normal chest and abdominal x-rays as well as an ultrasound but I guess those can miss something. She did have some blood and mucous in her poop that has since subsided on antibiotics but I guess there are different types of colitis including cancer-related types? Her nose was also bleeding when her platelets really dropped the first time so was that a symptom of the thrombocytopenia or was there another reason for that?
I never realized how difficult it would be to figure out the cause of this. I'd like to take her to a human hospital and give her an MRI or a CT Scan!