In addition to what Jamie and Idza have suggested, this article offers a "three-day approach" (towards the end of the article), which I thought is interesting. http://www.parents.com/toddlers-preschoolers/development/behavioral/bye-bye-binky-ending-the-pacifier-habit/ It involves informing your child that he/she will be saying goodbye to his/her pacifier in three days time. Repeat the same talk over the three days and act on it on the third day (via a game-like approach). Having the three-day timeline could prepare your child for the change and make it easier for him/her to accept it. However, at 18 months, you may have to make your child go cold turkey or try a more gradual approach (also mentioned in the same article), which is to slowly limit the use of her pacifier. You can try to first remove it during naptime, then extending to bedtime. Regardless which approach you try, there will be protests and crying. Do be mentally prepared for it because you have to be firm in order for your child to accept the change. Good luck!
Some parents choose to go cold turkey, but that does sound like it might be traumatising for your girl. You can tell her that she's a "big girl" now and "big girls" don't need pacifiers anymore. Let her say bye bye to the pacifier and put it away. You could let her suck on it during bedtime and put it away in the morning. I did that when I was a kid. http://sg.theasianparent.com/how-and-when-to-wean-from-pacifiers/
I suppose the best way to quit anything is to do it gradually with loads of encouragement. But I remembered as a child, my late grandmother would lightly lace my brother's pacifier (and mine probably) with lemon juice. We hated sour things back then and it worked!
thanks