Hey! Didn't know you were on this fandom too;
Well, about Ani. I think all the characters trust here because
1. She doesn't try to persuade ppl, just as u said. Even I wonder how they just fell for her
2. All the characters in the series have always made so many mistakes with each other; we know from the past two seasons that trusting anybody is not that easy. Everybody, everybody, Is having their own secrets, that always somehow, break free in the end but we know that is what this series is for, it helps to deal with issues and they are trying to bring up every issue.
And the reason why theh trust Ani, Is, as you said, dependent upon her being new. We know she craved to know things and that might be one of the reasons why she dragged herself into this; but if you see, there is no other person in the whole group whom everyone trusts. Clay is someone everyone likes, but he's been running about everyone and no one is gonna be disclosing anything like that.
And yes, tbh they should have all thought twice before trusting strangers, but I guess Ani was a bit persuasive.
And also, we needed to see Bryce's point of view, that's where this stranger (ani) comes in. We know no one in the group would have ever gone near to him.
But yes you're right. Ani isn't all that likable, she behaves like she knows everything and that was required for her character, maybe they just did that to add another issue of... pride? Overconfidence? Idk, but I did lile her when she was nerdy.