This section assumes you have unlocked Qiqi's Lucid Revelation buffs from the Witch's Revelation Quest: Instruction of Curious Form.
Qiqi is capable of providing not only extremely strong healing, but also decent Cryo Application and Energy generation. Not only can she now generate energy when the Herald of Frost hits enemies, but now her Skill has near 100% uptime, and performs coordiated attacks off-field.
Additionally, Qiqi is capable of providing potent buffs to the Stellar-Conduct reaction, so she is an excellent member to pair with Sandrone (who is currently the only character capable of enabling the Stellar-Conduct reaction, and thus creating a Polestar Field).
Regarding Weapon Choices:
Building Energy Recharge on Qiqi helps her use her Burst for better healing, as her Skill does not heal a whole lot on it's own.
Peak Patrol Song: Thanks to Qiqi's high Base DEF, you can get a meaningful amount of the buff from this weapon. While using this weapon, you must Normal Attack twice to activate the passive. DEF% stats can be considered if your team does not struggle with survivability.
Amenoma Kageuchi: This weapon will significantly improve Qiqi's healing capabilities, however, it takes lower priority over weapons that provide Energy Recharge.
Regarding Artifact Choices:
Sets
Scroll of the Hero of Cinder City (4): This set is a great option if Qiqi is placed in a party with a Natlan DPS. It should be noted that the DMG% buffs provided by the 4-Piece effect does not do anything in a Stellar-Conduct team.
Substats
CRIT Rate: Only recommended if using a Favonius weapon.