My grandma has alzheimers....im sobbing...help!?

My grandma was diagnosed with alzheimers one year ago. She still remembers me, but she doesn't remember all the times that I would come over to her house to sleep over and we would go shopping together. She would cometo my piano recitals and my birthdays. We wouldd always play the board game Trouble. I am crying right now, and mad that my mom (her daughter in law) keeps bringing her up. And my dad doesn't seem sad about his own mother. My mom arranged for me and grandma and her to go out shopping and do "girl stuff". I haven't done that with my grandma in a long time My mom just suddenly brought it up and said that Grandma was "so excited" and that just set me off crying. I feel like I have neglected her. I am scared and sad and I hate that she one day won't remember me! I cry every time I see her. Please help me! :( I am 14 years old