Something that never ceases to amaze me is that my mum, who is now pretty far down the road with AD just automatically remembers the words to songs very easily. She won't recall what she had for lunch or who visited or what our last piece of converstion was, two minutes earlier, but if I sing to her, more often than not she will join in with the songs and recall the words too. A favourite of hers is that song called 'Trees', as well as hymns and other standards from the thirties and forties. I can remember a day in her last home but one where there was a musical entertainment on and she seemed to just lift out of her dementia and become a cheery old lady again.
She did also have very lucid days, and even now I sometimes think she is more hindered in her conversation by deafness and a refusal to use a hearing aid, than by her dementia.
I think, if you have the stamina , that you should try to help stimulate the reminiscence through music and pictures and gentle conversation. You'll be amazed what happens, but remember that your mom is still likely to be forgetful and that the process does not, as Hazel says, go into reverse gear. Also she may get tired easily ( as may you) so take things in short bursts.