How to help suddenly-paranoid mother?

I'm a 53-year-old only child who had been living with my wife and daughters about 125 miles from my Mom (82), whom I would drive down to visit several times a year. She's been living alone since my Dad was confined to a nursing facility 7 years ago; he passed away last year just before COVID hit. I was visiting in October to help Mom out while she recovered from a bone graft to her jaw in preparation for dental implants, when she fell and broke a hip. And I've basically been living with her ever since, working remotely at my IT job from her house.

So she has a number of physical complaints (most recently, Bell's Palsy, which we found out after a stroke scare sent us to the ER), but had been fine mentally, apart from evident anxiety and depression, which she resisted my suggestion that she see a psychiatric professional about. There were a couple of incidents of anxiety-triggered delusions, one centered on the rehab facility where she stayed immediately after her hip replacement; the doctor there started her on Mirtazapine to help her fall and stay asleep at night. But she mostly seemed fine once she got home. Then on one of my weeks away, the first night she was alone she became convinced the house was on fire and called my cousin in the wee hours, who came over and found every light in the house on and Mom insisting she could see smoke where there wasn't any. A few days later when a friend of the family came to visit and stay with her overnight, she became convinced that the friend and I were conspiring to have her taken away. The morning I was due to come back she called in quick succession 7am to ask when, then called her sister and asked her to come over but she couldn't, then her cleaning service to see if they could come early, and then 911, due to apparently just an anxiety attack (I get those myself and have made plenty of unnecessary trips to the emergency room). It became clear that she had not slept hardly at all while I was gone, and even my first night back she didn't sleep - she was convinced that the white smoke, who it turned out had spoken to her once, was going to get her. The next day was Mother's Day and she did finally fall asleep and sleep most of the day ("best Mother's Day ever", she said) and all through that night; she seemed back to her old self Monday morning. But then Monday afternoon she started talking about the conspiracies again, was sure the police were coming to get her. During later lucid moments she said she thought at various times that the police thought she'd murdered Dad, that everyone thoughts was a witch using magic to make her cat do evil things, and a number of other delusions.

Her GP referred us to a psychiatrist and gave us a few Ativan to get us through any anxiety episodes until the appointment, but it really doped her up. The psych said that the delusions could come from sleep deprivation due to anxiety, and he didn't want to add to her cocktail of meds if he could help it. So he cancelled the Ativan and instead doubled her nightly dose of Mirtazapine, but gave us Buspar to take as needed.

Well, we've needed. And it hasn't helped, other than to also make her dopey (a full pill leaves her barely able to hold herself up on the walker) _and_ paranoid instead of just paranoid. Even with the doubled Mirtazapine she stays up at night, often fully clothed with her purse handy because the men in white coats or police are coming to take her away any minute. I know I'm supposed to reassure her without contradicting her delusions, but when her paranoia is centered on me and what she thinks is my dishonesty, I don't know how to do that! She keeps asking what she'll be allowed to take with her!

We have an appt with her GP tomorrow to go over a thyroid scan (she has a nodule that may be cancer) and I'm going to ask for a neuro consult; the psych suggested checking for a UTI but they did that in the ER. Meanwhile I'm at my wit's end and not sure what to do.

Any advice appreciated.