With a cold, it can take up to 2 weeks before it is completely gone. Having said that though, her cold symptoms may only appear for a few days.
There are over the counter medication you can get from the chemist to help with colds. Another thing is investing in a vapouriser. They're not cheap, but they do a fantastic job.
As for taking her to the dr, that's entirely up to you. If you feel better for taking her, then I'd suggest take her. At least then she can have a thorough check up, and the dr can give you some more advice.