Does Suisui take the sub DPS or healer slot in Yangyang SP teams?

I've read some comments on how Suisui fits into her team but I'm confused about what role she plays and how to add a third character to the Yangyang team because I don't know if they'd be filling an empty sub dps or healer role. I don't have Chisa.

TLDR is Suisui the healer (I then need a sub dps to make the team complete) or a subdps (I then need an extra healer) for Yangyang sp?