Hi R.!
It's not that this is your child, and that it was easier with other people's kids at your old preschool. I have one of these at home, and I didn't know how advanced she was either b/c she was our first. I agree that it is NOT a phase. I know it's really excruciating right now, but if you work really hard (and you will have to, for many years--sorry!) she will mellow out a bit as she gets older.
My daughter is now 8, and she was just like this. I was a stay-at-home mom too, so don't feel guilt about that. It didn't matter! My daughter would tantrum until she vomited (fun, right?).
I agree with this poster's comments:
"To be honest, she's just so smart and intense- she may never be an "easy" child. But she sure sounds interesting and funny (when she's not screaming, right?). And she will never bore you!
I think your instincts sound really good. Ignoring her doesn't seem to be working. I would never normally suggest a time out for this age, but maybe she's old enough to try one (as that other mama suggested)? You'd probably need to use a pack-n-play or something, to keep her contained for that 30 seconds or so."
For me, things got even worse when I had a new baby. By age 5, it had escalated to the point where I needed the guidance of a child psychologist to get a handle on her. He gave me handouts to follow which tiered the discipline--the ultimate being a time-out in a a previously chosen spot, for a set amount of time. I needed to tell her specific things. The key was to be extremely consistent so she always knew what to expect if she did x, y or z. It took about six months, but she really turned a corner.
Now she is still an intense girl, but she respects me completely, and also trusts me explicitly. She and my husband still go at it b/c he was never consistent. *sigh*
Definitely consider the 30-sec. time out in the pack n play (no toys, and don't use the crib b/c she associates that with bedtime and you don't want to mess that up! If you start now, maybe you can get a handle on her earlier than I did, but you may need to chat with a professional, b/c like my awesome, incredible daughter, yours is a force to be reckoned with. ;)
Hang in there, and hold on tight because it is a long ride. You are her world, and you can make it all work out, but everyone will need to be on the same page with you. Send me a message if you want to talk. I would be happy to do that. :)
Good luck!