My baby is 18months old. She has cough & flu. For the last 2 weeks. Went to the doctor and doctor gave her medication for flu & cough. But now she won't eat and she vomits every time she eats. Her vomit look like mucus, clear coloured mucus. Please advice me on this. I am so worried as she won't eat. Do I have to bring her to emergency right away??

First - I hope when you say 'went to the doctor' you mean your regular pediatrician or family doctor, who follows you through the years.
You call and leave a message with the staff, and they will pass it to the doctor, who will either call you back, or have someone call you back.
You can't possibly give enough history and current symptoms online.
If she has the flu, I hope you realize that a lot of caring for a baby's flu (or anyone's) is 99% home remedies. Rest, tons of liquids, sitting up, kept warm head to toe, no junk food, don't go anywhere, on and on.

However, given that she has started vomiting after 2 weeks, make that call!