There is a dispute as to what a Gallifreyan is. Some people believe that they are different from Time Lords, or Time Lords are a subspecies. Thus, the answer varies with one's definition of a Gallifreyan.
According to "The Doctor's Wife" at least one Time Lord, the Corsair, is known to have changed sexes more than once during regeneration. There is also a female incarnation of the Master who is known as Missy.