Why is my mom talking less and less?

This may be off base--but after I did chemo for cancer, one of the side effects that has not 'gone away' is my ability to recall names, words, whatever as quickly as I used to. It appears to be permanent. Doesn't help that my DH will tease me about it--he has really no idea how much harder it makes it to be standing there trying to remember the word for something and he's making stupid suggestions as to what I may be trying to talk about. (I know he does this b/c anything associated with the cancer still terrifies him.)

Be gentle with your mom at this stage. If she has any cognition left, let her have her dignity and give her a minute to gather her thoughts.

Closing her eyes? My daddy did this and it was sort of his way of re-grouping his thoughts as he slid deeper into Parkinson's.

Kindness is never wrong. Once I was unable to finish a thought and I was actually getting teared up over it--and my SON IN LAW reached over and took my hand. Didn't say anything, just held my hand for a minute. He intuitively knew that I just needed a moment.

I had a great aunt who had Alzheimers. She still recognized us in 2004. By 2005 she no longer recognized us and she stopped speaking. And yet she lived for 5 more years. She finally died in 2010 at age 100. The reason she lasted so long is because she had not a single other health care problem besides Alzheimers. I am sorry your relative cannot talk anymore. It is because she cannot. The Alzheimers has reached the stage where she has lost the ability to speak. Do not take it as a rejection. It is not. Treat her kindly and gently despite her not being able to talk.

Her brain is dying. Parts that control speech can be damaged or the parts that enable access to speech can be damaged or BOTH.

The closing the eyes is probably because she is getting overwhelmed by the things going on around her. My Mom did it too.

"sometimes she can’t think of the word , sometimes she expressed herself clearly, sometimes it’s a bit garbled. She has started using hand signals." This is all normal with Dementia.

Perhaps she is just starting to deteriorate a bit more? Just getting tired out and kind of done? Has this decline been gradual? Maybe call her doctor to get a better feeling for if this is "normal"? I think it probably is.

Often in late stage Alzheimer's people lose their ability to speak because of the deterioration of their brain. Comprehension of the spoken word can become an issue too. Her brain might also not be allowing her to open her eyes when she needs to, as the brain controls everything we do.
With that being said, don't be surprised if she soon forgets how to walk as well. I wish you the very best in caring for your mom.