It's just a phase. She's fine, really.
The best thing you can do is do your best to deal with it quickly and move on. Don't say anything unless she does. Just deal with everything pleasantly and be very matter-of-fact. Go through your normal morning routine. Just act like everything is fine. If she says anything (Mommy, I don't want to go to school.), be very brief in your response. "I know, sweety, but this is the way it is, and we have to go." If she get's upset, you really have to ignore it. When you take her to school, you have to be super quick. "Love you! Mommy has to go to work now. Have fun. Bye," and go.
Don't spend time talking to her about it or reassuring her or telling her she'll see her friends or anything. I know your mommy instincts are telling you to make her feel better, but it just makes it harder for her. I say this as a Mom who has done this way too many times. I try to remind myself to just be quick: walk in, hugs and kisses, go. But I just want to love him and make him happy!
My son has been going to daycare for about a year and a half. He loves it! He really does! But there are still days here and there when he just doesn't want to go. Maybe he's tired, maybe his tummy hurts a little, maybe he's just grumpy. There really isn't a deep, underlying reason. He's just not having a great morning and wishes he could stay home. We all have mornings like that. But as adults, we know that if we just force ourselves to get up, take a shower and get going that pretty soon we usually feel just fine. Kids don't know that, but I bet her daycare teachers will tell you that less than 5 minutes after you leave, she's just fine.
This is hurting you more than it's hurting her. Hugs and kisses, have a great day, Mommy loves you, out the door!
I know it's hard, but you can do it!!!