Quoting Emma and Chloe's Momma:" My 18 month old had a cold a little over a week ago. She's been better for about 2 or 3 days now. Last ... [snip!] ... her. It's just a little odd how fast it came on. I'm calling the doctor in the morning but they aren't that great at times."
I would do a walk in. My son was the same way around 2 and he had asthma. his cough would linger for about 2 weeks and sound like a smokers cough. he was very congested and just miserable. always wanted to be held. This may not be the case with you but you should take her in.