Teething could definitely be affecting your DD's sleep. Those molars can be killer. I also agree with a PP who said that taking an hour to nurse to sleep is often a sign that the child isn't tired enough. Is your DD still taking two naps a day? If so, it may be time to transition to one. If not, she may need a shorter nap, an earlier nap, a later bedtime, or more daytime vigorous activity.
However, once in a while, my DD will be quite tired but still seem to have a hard time nursing to sleep. It is almost like the act of nursing is keeping her from falling asleep. In those instances, I will ask her, "Do you want to just hold ummies instead?" If she says no, we'll keep nursing as long as she needs, but she will almost always say yes, put her hand on my chest, and drift to sleep almost immediately. I'm not sure what's causing it or why it is so rare, but it does happen maybe once a month. It didn't start occurring until she was over two years old, though, so maybe it's just one of the earliest stages in her nightweaning process.