First, you have a 21 month old. NOT a 2 year old. Really, those 3 months do make a difference. Not in terms of her verbal skills (since she's clearly got those down well), but in her experience, her ability to self-regulate (almost non-existent), her lack of impulse control.
Her behavior sounds very typical for an intense toddler. Instead of looking for outside 'causes' (you seem to have eliminated most of them), I would work on learning to deal with her outbursts and personality. For better or worse, that's what you've got to work with.
Right now, you're seeing all the 'negatives' in your personality traits. But clearly there are some positives too, right? Having high standards and being persistent are good things. For a 15 or 20 or 50 year old. They're hell in a 2 year old (for the parents). But who better to teach her to deal with these traits in a healthy way than you? She doesn't have to grow up with self-loathing.
I'm having our ds assessed for anxiety next week because anxiety runs rampant through my family and he's showing signs. Part of me is grieving because I really wish he could avoid this for him. Part of me is thankful that I know the signs and there are resources available now to help him.
FWIW, my niece was a child with high personal standards, intensity, sometimes aggression. My sister describes her standing next to the pool SCREAMING for 30 minutes because she wanted to jump in, but couldn't bring herself to do it. There was NOTHING her mom could do to help. She wanted to do it herself, but couldn't. Today, my niece is a beautiful, accomplished 20 year old taking high level science/math in college, playing piano beautifully, and singing in an a capella choir for fun. She has a very loving relationship with the sister that she nearly hugged to death (and nearly dropped a pumpkin on, and pushed over more times than you could count.) She's well adjusted, has good friends, and is quiet and very likable. This could be your daughter's future!
I've got some readings that I think you might benefit from. Some may be for yourself more so than your daughter because she's so young.Raising the Spirited ChildUnderstanding Your Child's TemperamentLiving with Your Active Alert ChildLiving with Intensity
(this is the one that's more for you)