Hi Cara,
So sorry to hear what you and your mom are going through. My mom also became very quiet, which we all found very frustrating. Now, I wonder if she was afraid to talk as her emotions may have gotten the better of her and she didn't want to upset us. My only advice is just to continue to talk to her. I wish I had talked more and shared what was in my heart with her.
Also know that this is not unusual, since my mom I have heard many say that not talking is common.