Hiya ccliffy and welcome to talking point.
The problem with your mum being in denial is very common. This can happen for many reasons including not remembering that they have been told, fear for the future, not recognising that she has any health issues at all. Overall though it is not though that the denial is deliberate. It is not by design and aimed at hacking you off.
You have to put yourself in her shoes and consider what benefits being constantly reminded that she has a life limiting illness would bring for her. The truth of the matter is that a diagnosis normally serves only two purposes. A..it is a gateway to gaining access to medication to slow down the progress of the disease and/or B it acts as a gateway to getting access to support services. So, on that basis there is no NEED for her to know anything is there?
You are right to consider the consequences of repeatedly reminding her that, outside of cancer, Dementia is probably high up on the list so far as diseases that no one wants to encounter! Despite some improvement in awareness of dementia have been achieved, there is still a huge stigma attached to the 'D' word particularly with older generations. For this reason alone I wouldn't tell her.
What you will find is that there is little that you can do for Dementia outside of making sure she takes any medication. What happens with most of us is that we deal with issues and challenges as they arise. As no two people have identical journeys with dementia this is the only realistic approach we can have as we never know what the day might bring. Tomorrow it might be her losing her keys, the next it might be her no longer being able to cook her own meals etc and on and on it goes. The challenge is to work to find solutions to all these things that your mum can cope with. That is where she needs your support. Whether you call it dementia or memory problems and she just calls it 'old age' doesn't matter at the end of the day. What is important to her is finding her keys and knowing that someone is going to prepare her lunch.
You might find the following thread of use to you as it gives you some insight into what your mum is experiencing and gives us tips on how we can modify our communications to make it easier for your mum.
http://forum.alzheimers.org.uk/show...ionate-Communication-with-the-Memory-Impaired
Hope this helps,
Fiona