Dear
@Betty65
It is hard to answer your question without a little more information. I have tried to answer as best I can and hopefully others will be along later.
1) Will your mother remember what is said to her by the doctor? If it will be immediately forgotten then little harm is done.
2) If your mum will remember and this will cause her ongoing distress I suggest you tell the doctor this. The way the news is given may well be changed, perhaps if the doctor is aware of this point. That will depend on the medical professional.
On the question of what benefit your mum will get from being told her diagnosis, based on your brief comments I would suggest little, if any, in terms of her actually knowing. Indeed if upset is likely please ensure the doctor is advised as stated above. Whether any treatment is then available I cannot say. My mum refuses to go back to the Memory Clinic so I am stuck with a diagnosis of Mild Cognitive Impairment from 2015. Most likely she has Vascular Dementia for which there is no treatment. Her condition worsens but mum does not want to know. As she told me once in a very emotional conversation “if I am going doally I do not want to know”. A different version of what you mum thinks. Hence I have no revised diagnosis, but a contented mum, just makes my carers journey a little harder. You would most likely be me if I had got us back to the Memory Clinic. With mixed Dementia not sure if any treatment is available.
If the doctor gives the diagnosis straight to your mother and there is upset consider the future. I refer to my mum’s blonde moments, we joke about her memory lapses, the Dementia word is never mentioned. Mum was initially in denial of her problem but as her understanding of her condition has weakened we have now slipped into “Anosognosia”. Please google that phrase. It makes it a little easier to understand where my mum now is, but does not get me any further forward in terms of the Memory Clinic. I will take my mum back when upset can no longer happen. I live with mum and care for her. I decided sometime ago there is no treatment for Vascular Dementia, it would destroy mum to be dragged back to the Memory Clinic so I will do it her way as regards caring. Her ongoing confidence and trust in me is vital to her welfare. I could not risk that relationship to get a paper diagnosis that would do nothing positive for mum.
Our circumstances are different but possibly similar in one important way. If mention of her condition will upset your mum then you will have to work around that. Offer help, support, etc, but always be mindful of the elephant in the room which cannot be talked about. In a strange way when the doctor talks to your mum it will be as much to you as it is your mum. The doctor ends the call and you and your mum are left to deal with her condition. My advice would be when talking to your mum accept her understanding of her condition, even if it is flat denial. In future just work around it in the practicalities of life. A formal diagnosis is a name for something, in terms of helping a loved one with Dementia it has little day to day practical value. In the end your relationship and how you can help your mum with her illness is a different thing.
Sorry but if a ramble but hopefully some help