What comes to mind is starting a pattern that gives her time to talk and gives you time to be alone...

I'm thinking something on the lines of, "I so enjoy spending time with you and I have about xx minutes today to talk...then I'm going to have some personal downtime"

It sounds like you enjoy some of the conversations...when the time draws near - let her know how nice it was to talk with her and your sure you can set some time aside to talk again another day."

Hopefully this will good for both of you?