I was just thinking: if we romanced Leliana with a manipulative Warden who cheated on her with Morrigan, hardened her and then defiled the Ashes (you can bully her into not attacking if she's hardened), it would explain her frosty yet concerned attitude towards Morrigan. It's possible the Warden will treat her just as badly.
That little scenario would also mean that she hasn't been truly loved by anyone but her mother. Marjolaine, Justinia and the Warden all used her for their own purposes. And Morrigan's childhood was horrible and isolated from contact.
Notice how they both have someone they dote upon: Josephine for Leliana and Kieran (possibly) for Morrigan. Leliana and Morrigan have in a common a great need to give and receive affection that was twisted and abused by someone in their background, Marjolaine and Flemeth respectively. They are both dreamers too. Leliana through her religion and she focuses on the future and change (her plans for the Chantry if made Divine) while for Morrigan it's through magic and she focuses on the past and preserving/rediscovering lost magic lore.
They have more in common than either would care to admit, I'm sure.