I respec’d her into Life Domain, then gave her the War Caster feat to help her concentration. Maxed Wis, put her Con to 16, and dumped STR.

For spells, use Beacon of Hope during combats where the party is going to take a lot of damage. It will maximize the amount they heal from her spells. Channel divinity and the Life domain spell list give you some fantastic options for keeping the rest of the party topped off on HP. She will get most of the healing spells from being Life domain, so you don’t have to fret the selection too much. Do pick up Healing Word and Mass Healing Word, though. They can be used to heal at a distance and as a bonus action, which can be useful.

When it comes time to do some hurting, my picks were Spirit Guardians (OP spell), Guiding Bolt, and Inflict Wounds. Banishment also came in clutch to put fights with bosses on hold while I cleaned up the mooks or did some healing.

Life domain gives her proficiency with heavy armor, so… that. And a shield. I can’t remember what items I’ve given her. Be on the lookout for things that either enhance her healing or give her healing a secondary effect, like granting Blade Ward for a turn.

Anyway, that’s how I’ve built her, and it’s worked well for me. I’ve only gone through the game on balanced, though. It’s possible this won’t work as well on tactician.