I don't know your mother's age from your posts, and if someone is going with her, but I would not trust much of what she is reporting to you if she is going alone- when you are sick and not feeling well, regardless of age, you don't tend to do a great job of keeping track of these things. She really needs someone to attend appointments with her and keep track of all the details, and keep a good record of who is saying what, when.
Sounds like that person can't be you- so who can it be?
My boss is dealing with this stuff right now (elderly mother is sick with stomach issues, lots of pain, getting the run around, lots of delay in getting appointments). At first her elderly father was attending all appointments, but he wasn't doing a great job of managing all the details. Now children are attending appointments, but due to the nature of them all still having FT jobs and lives of their own, they are taking turns, which adds another layer of miscommunication to the whole thing. They are seeing specialists in multiple hospital networks, so all the electronic charts are not talking.
If possible, can you do everything going forward in the same hospital system? That seems to be hugely helpful.
None of this stuff is easy.