I hope you will reconsider interpreting strong disagreement or phrasing that you don't like as "bad" and "irrational" and a personal attack on you before you meet with your kid's teacher. You may need to take a step or two emotionally back, if at all possible.
People can be attached to their children and still disagree about your course of action as you described. It's "irrational" to attack their credentials as attached parents and to throw away a whole website community because you didn't get the answer in the words you wanted. Look, we all overreact or are sensitive sometimes, especially when we're dealing with an issue that is really bothering us, so I don't fault you for the "I'm going away you guys are so mean" response, but I hope you'll rethink it when you have some time to calm down.
I also think that most people do not hide their dislike/suspicion as well as they think they do. By your own admission, you have viewed this teacher with mistrust and suspicion almost from day one. Please don't fool yourself that you haven't given her any clues. It may be why she is stiff/short with you (not that it excuses rudeness) because she is as wary of you as you are of her--and please think about whether or not you're so reactionary now that you're interpreting everything in the most dire light now. That too, is painfully obvious--even though most people think they hide it.
If I were you, I would ask to meet with her privately, not in the middle of class. I might consider apologizing that apparent you've both gotten off on the wrong foot, and for upsetting her during your visit (you didn't intend to upset her, did you? If not, you can certainly apologize for that and say it wasn't your intent). You could tell her that DD seems to be having some trouble adjusting, which worries you, and admit that you were hoping to observe your DD's behavior and reactions in the classroom. I would also ask her about the "tattletale" bit. Let's face it--1st and 2nd graders can be pretty annoying in their tale telling, and they do often need to be taught to be more discerning, but maybe there are better ways you can support your kids' (collectively) learning about that. I would wait to meet with her, though, until you are capable and willing to suspend your judgement and actually able to see her as a person in a non-combative and/or defensive way. Young teachers ARE often targets of parental bullies--you may not be, but you have no idea what she has had to deal with last year and with other parents, and just as you have made a knee jerk reactive judgement based on instinct, she is not subhuman and not doing that as well. If you are lucky, we can hope that she will also apologize for her tone once she understands that it hurt your feelings and upset YOU as well.
I would ask if there is any at home work that you could do. Some teachers, esp. new one, do need some time with overly strong boundaries (esp. after a bad experience or two) before they feel safe enough to relax them to something more livable for everyone. I have found that I can generally coax people out by offering to do grunt work that's not in the classroom, which gives me the opportunity to write a little happy note and turn it in--it builds bridges, and shows that you're interested in things other than checking up on her (fake it until you make it). If you're unwilling to put in the time trying to work things out in a way that respects her comfort as well, then I guess you might as well persue a class change--though IME those are really difficult to get.
I don't think it's too late to try and "start over" with each other. But you have to be willing to do it (and so does she). I've found that admitting you didn't get off to the best start, that obviously you've both hurt feelings and had misunderstandings about the other's intentions can really help things get back on track. I'd at least try to do it. Maybe she is a terrible person, but I'm going to guess that probably she isn't. It's worth a try, what do you have to lose?