While I agree that you should check into the daycare to see if anything has changed there, the reality is that she is 2-1/2 and is going to change her routine as quickly as the weather in some places. Figuring out what the root of the problem is isn't always where you find the solution. Daycare may not be the problem at all. I have a few suggestions:
1. Take her in whatever she is wearing when it is time to go. I have taken my kids to pre-school in their pajamas, in their undies, without shoes, etc., because we were going no matter what. While they may have gotten in the car in a state of undress (and frustration), they immediately changed their minds about going into the classroom in their pjs or without the appropriate clothing when they realized that their friends would see them this way and may not be able to participate in activities.
2. Challenge her. My adorable now 6 year old daughter (we call her Sunshine Girl) is rather stubborn and enjoys playing rather than doing what she is supposed to be doing (getting dressed, brushing teeth, etc.). I have found that challenging her to do something by saying I can do the same thing faster is a great motivator. She almost always "wins", but there are times when she amazes me with how quickly she does this.
3. Have her participate in choices. Giving her choices about what to wear and deciding the night before helps. If she changes her mind in the morning, then you make the decision about allowing her to choose from the other outfits or reminding her that she made her choice. I would go with the former, since forcing her to stick with a choice she made the night before could lead to more of a tantrum.
I hope that this helps you tame the mornings.