B.R.
I had troubles with 2 of my 3 daughters with the clothing issue. They were a couple of years younger that yours but I would still do the same thing. What worked for me was going through the motions of picking something out the night before, letting her change her mind in the morning, her still not wanting to get dressed, then saying that Mommy's van is leaving for school in 5 minutes and of course she will be going with me, whether she has clothes on or not! After driving her to school in nothing but her panties a couple of times she got the idea that she had to wear clothes and that Mommy wasn't going to change that. I obviously packed a set of clothes for her to put on in the van. There were some pretty cold mornings that we did this, so I also made sure there was a blanket in the van for her. Once we got to school I would ask her questions like "Is everyone else wearing clothes, What will all the other kids think about her being in her panties?" Of course I would never let it go that far, but she doesn't know that.
Also, be sure that your not picky about the outfits she wants to wear... by that I mean, if she wants to wear stripes with polkadots, let her. If she won't wear something weather appropriate, let her experience the natural consequences of doing so. If I felt it should be different I suggested "It is cold out side, so you might like to wear pants under your dress or shorts" Don't use "You have to...." if you can keep from doing so. If she still refuses tell her "OK you don't have to wear that but let's put it in your backpack so that you can put it on later if you choose too".
It took about 1 week of doing this and didn't have another problem after that. She got dressed when she was told and she got to pick out whatever she wanted.
Another thing I noticed with one of mine is that she has a hard time selecting anything if there are too many options. So I put all of her out of season clothes in another closet, but accessible. She may remember she has a summer outfit and want to wear it in the dead of winter, but usually it's out of site out of mind.
Hope some of that helps. I know it's challenging. They need to feel like they are in control, with actually letting them be in control.