How do I help my grandma with her sadness over dementia?

My 82-year-old grandma was just recently diagnosed with dementia and was prescribed Memantine. She is in the early stages between "mild" and "moderate." She is still very aware of what is going on with her health and is having difficulty accepting it.

She's the most intelligent person I know, but her age is catching up with her. Within the past 5 years, her health (physical and mental) has deteriorated rapidly. She is also the most stubborn person I know. We have a close relationship, but my mother is the only person who she lets see how her changes in health have affected her outlook on life. Whenever I visit, she always tells me that she's okay, as to not worry me... but my mom tells me that she is struggling.

I want to be able to make it so that she feels comfortable expressing her true feelings and thoughts with me. I think if she could/would, I could help her enjoy life a little bit at a time. Then, there is figuring out how I do that!

I know these are very broad questions but I have to ask: How can I get her to open up to me without her feeling interrogated? What are the right questions? How can I help her feel better about her mental state? What are some ways I can help her have joy in her life again?

I really appreciate any response. Thank you.