Highlighted weapons are free options.
Shenhe is a Support for Cryo characters, capable of providing damage buffs from her Skill and dealing damage while providing Cryo and Physical resistance shred from her Burst. Her Skill gives a few stacks of additional flat damage bonus to all nearby party members (5 stacks on Tap and 7 stacks on Hold). This additional flat damage bonus only works on Cryo attacks, so characters who don't use Cryo attacks don't benefit from Shenhe's Skill, do note that Cryo infusion from Anemo characters does act as a Cryo attack, so it benefits from Shenhe's Skill. Another thing to note is that the additional flat damage bonus Shenhe provides uses Shenhe's current ATK, so it doesn't snapshot.
Shenhe's Tap Skill gives a teamwide 15% DMG boost to Skill and Burst DMG. This lasts 10 seconds.
Shenhe's Hold Skill gives a teamwide 15% DMG boost to Normal Attack, Charged Attack, and Plunge Attack DMG. This lasts 15 seconds.