Litltle rash

If the rash is flat and red don't worry. It may just be a heat rash or be from clothes rubbing. If you changed detergent or diapers recently she may be allergic. Have you given her any new foods? May be a food allergy. Watch for any swelling or problems breathing. If it seems to be bothering her you could put some A & D ointment on it. If the rash is raised or has red streaks coming from it get an appointment with your pediatrition tomorrow - it may need a doctors care.
If it hasn't gone away in a couple days take her in to doctor.

This also maybe chickenpox they mainly start on the trunk and legs if your child was already vaccinated you might just be getting a small case if it is lasting for more than 2 days absolutely take her to the doctors

Watch to make sure it doesnt spread, and give her some benedryl, if it gets worse call dr.