The place my mother uses in FL changes her appointments for this sort of thing sometimes. My mother has a lot of things going on health-wise; she sees more docs in a year than I've seen in my life.
One time the doc over-scheduled a colonoscopy for a patient with cancer when the scheduler had already filled the two rooms. Another time the tech who was trained to do assist with her Mohs surgery had an emergency and they didn't have someone else available to step in. Last year, her surgeon's wife and kids were in a nasty accident and she had her Mohs rescheduled.
My mother is awful about misplacing her cell, so sometimes they call me as her "emergency contact" to try and get in touch with her.
it's possible, but a little weird. the doctors office usually has nothing to do with scheduling MRIs and CTs. a CT is definitely not an all day affair.
Is it possible that they have slots open up earlier and they are asking her if she would like to come in earlier? Or is she not getting a choice?
Also, if these tests are at a hospital, she may be getting bumped for more urgent patients. Cam she try to get some of her tests done at free standing MRI places, etc? Or the weekend when it tends to be a bit less busy.
When I worked at the hospital there were lots of no shows for earlier morning tests. I didn't do scheduling for that department but I was in charge of greeting these patients at the door and escorting them where they needed to go. I think cancellation is common but I don't remember meeting patients at their nonspecified time due to cancellations earlier in the day.
That did happen to me once when I had an endoscopy, but they moved the time up by something like an hour, not half a day. They just called to confirm and said "Yeah, we need you to come check in at 7:30 instead of 8:15." I have had more tests done up at the hospital than I could begin to count, though, and it's only happened that once. I would have a really hard time believing someone saying that it's a significant time change and it happens for every appointment.
Can you have her start bringing in proof of the appointment changes?