Aren't Shadowheart's (and all of the companion's) romance scenes/moments gated by approval and some dialogue choices you've made along the way? Did you actually check what was your approval with her before the party? Have you discussed her Shar beliefs with her? Triggered all the other Shar related scenes with her (like the one in the owlbear cave)?
For example with Astarion, he'll laugh at you suggesting romance if you are below medium (and even at lower ends of medium he'll refuse if you bring it up). Same goes for Lae'zel - even if you've met with her gith kin, she might still say - no, I don't like you even though during her initial conversation start at the party she sounds ready to jump your bones, if you say - sure, she's gonna be like - 'err actually no'.
Best way into someone's pants is through... bringing them along with you on the journey. Who would've thought?
But on a serious note - you can't bang SH (as of now anyway), all you can do with her is drink some wine, watch some stars and kiss. That's all.
Yes I know every conversation, and what to say to get approval. I checked all the boxes besides 1 miss.
