New ETA: So now we have an appointment with the neurosurgeon in the other hospital in another city for Thursday. This appointment was set up by our neurosurgeon contacting that neurosurgeon, but luckily this process has been approved by the insurance company. So now we don't actually know when the surgery will be, but based on the severity of the tumor, it should be within a few days of the initial appointment, hopefully Friday.
I have read all of your comments, and even though I've only replied to a few, I really really appreciate them. All your thoughts, prayers, and vibes are greatly appreciated.
ETA: Right now, the plan is for my mom to go to another hospital, with another neurosurgeon, in a city about an hour away. To the best of my knowledge, she's entering the hospital via the ER, but she's taking copies of her medical records and tests from her own hospital, so hopefully they won't need to redo those. In the ER, they should be like, "This woman has a brain tumor! Operate immediately!"