I don't know what to do

Ok, so, here's the thing. My grandma has Alzheimer's and it's getting worse. She lives next door with my mom ( we're sharing the same yard). While my mom's at work, she keeps on walking into my house (where my husband and I live) and says that she wanna go home and that I should open the front door so she could leave (she doesn't have a key of her own cause once she's out she might not remember how to come back home, so we don't wanna take that risk). I simply don't know what to do.. I know it ain't her fault, I know she's doesn't know what she's doing, but she keeps on appearing in my kitchen wanting the key so she could leave. And this is happening several times a day. She's better when my mom's home, but that's usually in the afternoon. I know I shouldn't be annoyed by this, I should be understanding, but it's getting in my daily activities.. It's just been a lot lately and I quess I just needed to write this down.