My group is doing a campaign from Shadow of the Dragon Queen. I was planning for my character to be a healer who is a former cleric of Takhisis who rejected her Queen, but I am not sure how to actually build the character. Is there a certain cleric domain I should look into, or should I consider another class?

Thoughts?

build it like any other cleric. sounds more like back story 

If she no longer follows Takhisis, where does she derive her power from? If there is no god she would follow, what about an ideology? Use these as a guide for your cleric's domain. If none of these work, consider not making her a cleric.

Seems to me like they fit the life domain. Have them pick a new deity that they serve and they might always be trying to please their god and prove their devotion to them. 

Serious ideas:

1. A Life domain cleric who's concerned about saving lives above anything else. After a battle, they'll heal enemies if they don't serve a threat. At the same time, if an ally will bring about much death and destruction, they'll take them down. (Obviously doesn't work with party members, it's more for conversations.)
2. A Grave domain cleric (another best-in-class healer, along with the Life domain) who's seen enough death to know that they want to bring comfort to those left behind—someone with great empathy for the grieving, even families of enemies.
3. A Trickery domain cleric who believes that the existing power structures are unjust and need to be destabilized to allow a more natural redistribution of power to occur. Hard chaotic good and seeks to cause confusion wherever there's order.
4. A War domain cleric who was trained to help with the military found that it was too extreme even for them and now works to make sure a band of rebels is prepared to fight for their freedom. Someone really concerned with training others and making sure they have what they need in case they're attacked.

Funny ideas:

1. A Life domain cleric who thinks life and love are intertwined and considers sex to be an act of worship.
2. A Death domain cleric who's very concerned about others creating unauthorized undead. They seek out necromancers and demand to know who authorized this, and strike them down if they don't have the proper credentials.
3. A Forge domain cleric who creates amazing weapons and armor, but etches inappropriate things onto everything he creates. This can extend into carving things into tables and walls too.
4. A Nature domain cleric who wants everything to be in its natural state, which manifests in them taking their clothes off at inappropriate times so they can be au naturel. 

To point out one missed by above:

Order Domain would be a serious idea