Dear Z.,
I just want to say that I can SOO relate to what you're dealing with -- and your description was hilarious! My 2.5-year-old son is going through a big "I don't like" phase, as in, "I don't like pants" (all pants), "I don't like sweater" (all sweaters), I don't like breakfast, dinner," etc. My friend even gave my son a very hip, expensive-looking sweatshirt for a gift, and my previously sweet, mellow little boy embarrassed me horribly by shouting "I don't like this shirt," throwing it down, and stomping on it....
I haven't found the magic cure myself, but I really like Meg's suggestions. Two more random thoughts that you may want to try (please let me know if they work):
1. What about getting one of those little portable kitchen timers, bringing it up to your daughter's room, and setting it for about 3 or 5 minutes. You can say something like "When the timer buzzes, it's time to go down for breakfast, so we have to run, run, run and pick out your clothes for the day." That might change the rhythm of the morning enough to break the spell, and the timer might have enough "authority" to get your daughter focused on something else.
2. You might consider just allowing pajamas until it's time to take your daughter shopping for spring clothes. If you involve her enough in choosing her new clothes, she may feel good about wearing them.
3. Finally, this isn't really a suggestion, but more than half the little girls in my son's preschool seem to wear "princess" costumes every single day. They run around with these pink, shiny, lacy acrylic dresses over their snowpants. So I suspect you're not alone.
4. Finally, finally, it just occurred to me, is there a chance your daughter is just cold? She might want something cozy, or not want to change at all, b/c your home temperature isn't set perfectly for her internal thermostat....
Hope this helps, and sorry to ramble!
Mira