When does Leah discuss "Tristram", "Leah's Childhood", and "About the Temple"?
Solution 1:
"Tristram" is available during The Fallen Star
"Leah's Childhood" and "About the Temple" first show during The Broken Blade, but are also available at the beginning of Trailing the Coven
Solution 2:
To get "Tristram" do the level in the first act where you have to go to Adrias hut, and into her underground lair, kill the ghouls etc and talk with leah to complete the quest, after the quest is completed, talk with her again and the Tristram dialogue should be there.