My wifes lips have swelled a little she's 12 weeks pregnant..why.?

Labial swelling: A couple of things. One would be vulvitis or infection/inflammation of the labia. See your OB or midwife to exclude that. Later in pregnancy you may see swelling from fluid retention called edema in the labia, though more common seen in labor. She also should have the labial glands examined as a bartholin's cyst/abscess can occur as well.