Talking to paranoid Mom's Dr with her present...

My mom is not diagnosed, but I have no doubt she's in the early stages of dementia (or something with similar symptoms). I moved her in with me because her former neighbor told me he caught her climbing off her roof, alone, onto a precariously placed ladder, because she was looking for a recording device that some homeless people had placed up there to spy on her. It has been a few months, and now she's looking to move several hours away. I feel like I have a small window of opportunity here to get her to agree to receiving help before she's too far gone and causing big problems. The problem is, she's in complete denial - or can't recognize that anything is wrong.

The last time she went to a doctor's appointment, I said I would appreciate it if she talked to him about a cognitive assessment. This was met with anger, frustration, paranoia, and cruel accusations (which is, sadly, becoming quite common). When she got back from her appointment, she said the doctor had given her a test "and there's nothing wrong with me", and he asked me to come to her next appointment - I assumed to discuss alleged cognitive symptoms. The following day (which is important because she often has nighttime hallucinations that she thinks really happened) she told me that she mentioned a financial stressor, then the doctor suggested that might disqualify her from Medicaid and that she should consider getting a lawyer. This stressed her immensely and she didn't want to go back - mentioning that she might get arrested if she did. Later, when I brought up making the followup appointment, she talked her way out of it in every way that she could - it was only to check her medication and she felt that was fine; it was only to talk about her stress, but she's not stressed any more, etc. I had to stick to the idea that I was concerned about the idea of losing Medicaid and wanted to get that straightened out. As she got more upset and flustered, she said "is this just because you want me to take the longer test?" I'm assuming that's a more-in-depth cognitive assessment that I hadn't known about. That's what makes me think there's more to my being invited to this appointment than the doctor inquiring about household finances. She eventually, very angrily, scheduled the appointment.

My question is, how am I supposed to discuss her symptoms with her doctor, with her present, without causing stress/problems? She used to ask me to point out symptoms I noticed, because Alzheimer's runs in the family, but when I started to, she would blow it off and then start hiding those behaviors from me. She also had a dream/hallucination (that she thought was real) in which I yelled at her for many of her symptoms, she said "it was crushing to hear", then thought I was going to sue her for it. And like I said earlier, she often gets extremely upset and defensive. Now I'm going to team up with her doctor, right in front of her, and say all those "crushing" things that she doesn't believe are true. However, I feel like it's my only chance to escalate myself to the level of caretaker - if her doctor facilitates it. I can't talk to him in private if she doesn't sign the proper forms, and she won't sign them if she thinks nothing is wrong. I know I can't force things to go my way, but I feel like I at least have to try right now, before she moves away and falls off her roof or something. Any recommendations, suggestions, ideas, or commiseration would be appreciated. Thanks.