Hi Katie, I take care of My 93 yr old Mother & can tell you from personal experience that it doesn't make any diference what or even if there is much of a conversation. The important thing is just to visit her & let her know you Love her (it will make you feel good too).
My Mom can't follow conversations very well, but she gets very excited whenever someone stops by to see her.
Some days she may participate in a conversation, some days, she won't & some days a conversation (the same one she enjoyed a day ago) will agitate her. The length of time you visit can be short enven 5-10 minutes (in fact sometimes that is best.
Tell her about school, the weather, or just that you Love her.