Isn't that with the assumtion that peoples true colors are horrible. Thats just not always the case my friend. It does not sound like you are building a rapport, but rather wearing the person down. That is probably why you assume horrible people are nice and nice people are posion. I don't know you so I have nothing more to say about that.
All I can say is don't expect to be happy if you have to "work" for anything with people. It puts you in a bad and unnecessary spot.
Stress and fear is what gets you killed. Keeping a cool head and think things through is the way. Why be hostile? No time for any bs drama including rudeness. Emotional instability. Nothing interesting or useful in that. It is a reason to leave her ass on a grove corner. If she was actually good with secrets she would say very little and follow along and subtlety take whatever. In which case I'd leave her 8 int ass anyway. Lol
The only way is to cut the rude bs and join the team like a normal tadpole infectee.
I would not even think about trust in Shadowheart's case since its literally join me or die from several things that have nothing to do with me including whats in her pocket.
I said some people, do not misinterpret. We had wide spectrum of companion's characters, now some of them lost their uniqueness. And working on trust is normal thing when person has her baggage like SH. She was guarded and opened because of our actions. Now they removed it, she became more flat. @Nyloth pointed the thing with Astarion, similar problem.
What kind of progression is left for SH? Show her true colors as evil priestess. We have Gale, he's kind but very manipulative.
What devs could do is cutting some of disapproves, giving at least one good companion and leaving VA untouched. Now its a mess.