Shart's almost entirely irrelevant for Act 3, other than one big fight for/against the Sharrans (which you can ignore), for act 1/2, she's mostly there for exposition and build-up for the Ketheric conflict. Without making the Selune/Shar lore and conflict relevant to the player experience, Ketheric's presence as the first maj🐻or antagonist would be a lot less impactful. If you REALLY don't like her, all you have to do is not let her join the party, and tolerate a few interactions for plot advancement. Laezel and Gale are just as important and unavoidable as she is, so to single her out is definitely a personal issue and not honest criticism of the game.