So if it reached that, it would actually be the end of a rather long process. (DD1's 4 now, and there's much less rigmarole, although still some, depending on the day. Other days I can ask her to go get dressed and get back a suitably dressed child.)
We eat breakfast in pyjamas, so I'd start by saying it's time to go upstairs to get dressed. If she refused, I'd give her a choice of two ways to go up the stairs (walk, crawl, slither, be carried, whatever I think might tempt her in that moment). If that doesn't work, I say I'm going to count to 3, and then I'm going to choose for her. If I get that far, I choose 'be carried', and I'll do it. Similar pattern for the process of actually getting dressed, this shirt or that shirt, and so on, although I might mix in a little bit of random silliness as well, pretending her trousers go on her head or that I've found a frog in her sock, or whatever. It's difficult to be defiant when you're laughing. (This extends to physically defiant, if they're laughing, they're generally too distracted to put up much resistance to you popping a shirt over their head, etc.)
It feels like an awful lot of talking for a basic task, but if you keep it going at a decent pace (don't give a million chances, this or that, 1-2-3, I choose), it doesn't actually take that long – probably less than what you're doing now, although I guess maybe you get something else done whilst she's in her cot.
If, however, she really isn't cooperating one day, and you do reach the point of needing to say 'right, come get dressed now, or you're going to nursery in your pyjamas', she might well initially be delighted. But you still achieve a number of things – you get to work on time, for one, and she sees that you can handle this. She threw peak resistance at you, and you shrugged and took her in her pyjamas. If you have a good nursery or childminder, I think they'll then back you up (and will have seen it all before), something like a little gentle disapproval that wasn't that silly not to get dressed with Mummy, now she has to go get dressed instead of getting stuck into whatever tempting activity is set up. And at the end of the day, pyjamas are not actually very different from a t-shirt and leggings.