Whom also wanted to change things. She just couldn't because of the current situation. Now with the Inquisitions backing, changes can be made. The previous Divine wanted to loosen the leash on the mages, and wanted to turn the Chantry back into something that helped the people, and not just tell them how to live. Cassandra also wants the same of the Chantry. Helping people. Not governing them. You can do this, you can't do that. She doesn't want that. I see no reason why it can't stretch to the people who spread the Chant as well.
Heh, I don't think Chantry members having relations was on Justinia's to-do list.

The point being, such a notion of change would be prompted by purely selfish reasons and Cass is not a selfish woman. When one enters the chantry they give themselves over to it and the Maker, they are supposed to hold him above everything else. The divine is essentially "married" to the Maker, that is her relationship. She would literally being going against the the base foundations of her position. Cassandra is too faithful for such a thing.
It would mean that she is too weak a person to fulfil the role she has ascended to. She would not see herself as worthy if she couldn't even abstain from a romantic relationship. I think it would play on her conscience a great deal and I wouldn't want her to be living the rest of her life in guilt.