Your daughter sounds exactly like mine at that age, she was extremely high maintenance from day 1, her "terrible twos" were loooong, and she was a terror (or rather, she tried to be) from 18 months to 3.5.
Basically, i began not giving in to her at all by 18 months. On one hand she was super intelligent, changed her own diaper so I knew she was ready to potty train, (at least the peeing, pooping took until she was 3) and her vocabulary, counting, and ability to hold full conversations with anyone was astounding. But she was, as you say, "spirited", and had already learned how to get her way. Our pediatrician was the one who said his advice was to start training her to behave, at 17 months.
So, I began teaching her what "no" meant in regards to what she was allowed to do, told her what was expected of her at home or when we went shopping, on walks, to restaurants, etc., and she was expected to follow the rules or there were swift consequences like time outs or losing a privilege. If she acted up or began to scream I took her outside, made sure she wasn't hungry, thirsty or needing to potty, talked to her about her behavior and what she needed to do, and we then went back in to finish what we'd been doing, we didn't leave. By the time my friends with children her age began pulling their hair out from their toddler's antics, they marveled at how well-behaved my daughter was.
It wasn't annoying when other mothers complained about children like her or their moms, because I didn't want her to be that way, either! I never wanted sympathy or understanding, because other parents have their own issues to deal with. She was healthy, bright, and a natural learner, and I thanked God for those things. I had options, to deal with her and her behavior, or lack thereof. I don't feel badly for moms with children like her, I feel badly for the kids who are allowed to be that way.
Yes, it took a LOT of work on my part, my older child, a son, had been so easy-going and obedient. But I had to be consistent each and every time and follow through on what I'd said, or she would have walked all over me. And when she was about 15 she told me that she appreciated the way I didn't let her get away with things from the time she was little like other parents did. She was very insightful : )
My 27 month old is a handful, not nearly as difficult as her, though, and we've been working on his behavior for sometime as well. The more set in their ways they get, the harder it is to undo the behavior, I guess I want to deal with it now, rather than later ; )