My pediatrician (and dentist both) told me that my son needed to be off the paci around the age of three, just because it can affect teeth development if the child is still using it when the permanent teeth come in, and kids can begin getting their adult teeth any time after their third birthday (my four year old doesn't have any yet, though). My pediatrician pointed out that many kids give up the paci only to begin sucking their thumbs, and unlike the paci, you can't take a thumb away from them. Something that I personally think is key to stress-free parenting is letting kids move at their own pace, so you might watch for signs that your daughter is ready to give up the paci, and then move when the mood is right.
Some of the questions the others have asked are valid. Is your daughter using the paci to help get herself to sleep, or is she sucking on it all the time? If she's using it even when not trying to sleep, now's a good time to start weaning her off of it. I am a big fan of weaning. I think it is easier on everyone involved.
I began weaning both of my kids at age two, and it works out nicely because they are old enough to understand that the paci just stays in the bed. No arguments, but be understanding about the adjustment. For the first couple of weeks, I let my kids climb into the bed any time they want the paci. This way, they accept that the paci has to stay in bed, and when they feel overwhelmed or need to soothe, they can still use it. Both of my children asked to get in their beds a lot in the beginning, and within a month or two, were not asking to get in their bed (except when sleepy) at all. They slowly learned to soothe in other ways.
Once this has been accomplished, then you can begin weaning off the paci at night as well. I haven't weaned my daughter all the way yet, even though she is signalling that she may not need the paci anymore (she's two and a half, and sick at the moment - I plan to start as soon as she's feeling better, probably next week sometime). My son was an extremely easy experience, despite that he was addicted, as well. We started taking his paci away after he fell asleep at night, so that he didn't have it in the middle of the night. We talked to him about how pacis are for babies, and what a big kid he is now. We started talking about doing things together that only big kids can do. We gave him an altered and unsatisfactory paci at night. After three nights, he didn't need it anymore.
We moved at his pace, which made it a more drawn-out experience, but almost completely stress-free.
Good luck to you.