I feel your pain! This has happened to me several times in the last 8 months (DD is currently 19 months old). She had to re-adjust her latch with the 1-year molars and each of the canines. It seems like the new teeth not only hurt as they come in, but also change the internal shape of the mouth, and she has to learn to nurse around them. During the adjustment period her jaw seems to be angled awkwardly, and she doesn't have her usual finesse, so I get bruised and bitten. It takes a week or so for her to get used to the new "equipment," and then she stops hurting me.
It helps me to think of it as a natural awkwardness, like someone driving a car they're not familiar with or learning to drive stick or something! I just try to have compassion for her... and especially to repeat over and over that she's not hurting me on purpose!