My son has a similar ultra sensitivity to sound and other sensory experiences. He is within the autism spectrum however. I would definately contact your pediatrician. I'm not saying that your daughter is autistic, but since the sense of smell is something controlled in the brain, and especially since this is something that you haven't noticed before, you may want to ask your pediatrician about it to be safe.
There is a program in Hudson Wisconsin for children with over/underreation to senses. There might be something up in northern Minnesota that is similar. Your pediatrician would know. You may also try contacting your school district. I started the evaluation process for my son through the school district and they were wonderful and so helpful.
Any time something worries you, it doesn't hurt to contact your doctor. The worse thing that could happen is the doctor will say its a phase and you'll feel a little foolish. But if you feel troubled by it, you should definately look into it.
Good luck.