GUNH could simply mean "woman" in Mt. 5:28. I guess my judgment is based, in part, on F. Danker's understanding of the term in the Matthean verse, but it makes sense to me that Jesus could be referring to a married woman in view of the OT decalogue command prohibiting covetousness respecting another man's wife. On the other hand, Job exclaimed that he concluded a covenant with his eyes so that he might not be inappropriately attentive toward a young maiden or virgin (Job 31:1ff). Then again, Jesus' mention of adultery in this verse may point to GUNH signifying "wife" here. The Expositor's Greek Testament suggests that GUNH could refer to a married or unmarried woman in Mt. 5:28, as does M. Zerwick's Grammatical Analysis of the Greek New Testament. In any event, if we're going to base our understanding on context in other passages that contain GUNH, could not the same methodology work for 5:28? Compare 1 Tim. 3:11? See also 1 Cor. 5:1.
Expositor's Greek Testament: Matthew 5:28.—ὁ βλέπων: the looker is supposed to be a husband who by his look wrongs his own wife.—γυναῖκα: married or unmarried.