These talents will provide the biggest boost to damage. However, with this ability instead of strength cunning will be used if it is higher. How this works: generally the damage for rogues is calculated from strength and dexterity. Get Lethality as it will boost your damage. This will allow you to unlock chests for additional loot and gold. Due to this, I recommend getting Device Mastery as soon as possible. My guess would be that Leliana will be the only character with high Lockpicking ability in your party at the time you get her. It will provide increased damage, attack, and critical chance benefitting them directly
What is left you can put into Survival.After that invest to 3-4 levels into Tactics so that AI could comfortably use all the needed talents.Master Combat training, this row will provide: bonuses to attack, armor, and higher tier weapon talents.You can also invest in the constitution for more survivability, but I view it more as a waste of points for this type of character as it should be avoiding direct combat. Moreover, after you get Lethality talent it will boost your damage directly. Cunning will boost your songs increasing the bonuses that they provide. Third priority - Cunning - after you have 34 dexterity, put all points into this stat.It will also boost your attack, damage, and defense You will need it to use the best bows in the game and to get all the required talents. Second priority - Dexterity – get it to 34 points.18 points is also an option if you get bonus strength from other equipment: belts, rings, amulets. You will need it to wear end-game light armor. I suggest this investment into attributes: Moreover, to wear some of the best armors at the end game you will need strength.
As Leliana is a rogue, your main attributes are dexterity and cunning.