Surprise: the earliest technical drawing we have was created by a woman. The Greeks had very likely created some sort of technical drawing and the frescoes of the Romans demonstrate that they were certainly capable of creating drawings, but the medieval vicissitudes halted the train of transmission. Instead, we have one drawing of two women grinding grain at a mill.
This drawing is contained in the "Hortus Deliciarum," an illustrated medieval work that was a large compendium of (primarily biblical) knowledge. The work was commissioned and probably executed by the Abbess, Herrad von Landsberg. The drawing is notable because it is atypical for the work as a whole. Other than a depiction of two men plowing a field, a map of Stuttgart, and a depiction of various types of shoes, the rest of this substantial book is dedicated to illustrating theological topics.
To say that we actually have these drawings is a bit of a mistake. The original manuscript was burned when Stuttgart was bombed in 1870. Instead of the originals we have copies from two different researchers. I am a bit loath to credit these copies as completely faithful. Ferguson, for example, demonstrates how copies of Francesco di Giorgio Martini's drawings were corrupted due to the limited technical understanding of the copyists. Similarly, Chinese copies of Besson and Ramelli are notoriously corrupt. At the very least, we can assume that since the copies of the Abbess's efforts were executed in the nineteenth century, the copyists could understand both the technical operation of a medieval mill and the rather unique approach to perspective.
Herrad used the drawing in question to illustrate Christ's comments on servants, particularly Luke 17:35 and Matthew 24:41:
From Matthew 24 (I've used my personal favourite: the KJV. The Abbess, of course, would have used a different version!):
36 But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only.
37 But as the days of Noah were, so shall also the coming of the Son of man be.
38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noah entered into the ark,
39 and knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.
40 Then shall two be in the field; the one shall be taken, and the other left.
41 Two women shall be grinding at the mill; the one shall be taken, and the other left.
42 Watch therefore; for ye know not what hour your Lord doth come.
43 But know this, that if the goodman of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up.
44 Therefore be ye also ready: for in such an hour as ye think not the Son of man cometh.
And from Luke 17:
33 Whosoever shall seek to save his life shall lose it; and whosoever shall lose his life shall preserve it. Mt. 10.39 ; 16.25 · Mk. 8.35 · Lk. 9.24 · Joh. 12.25
34 I tell you, in that night there shall be two men in one bed; the one shall be taken, and the other shall be left.
35 Two women shall be grinding together; the one shall be taken, and the other left.
36 Two men shall be in the field; the one shall be taken, and the other left.
37 And they answered and said unto him, Where, Lord? And he said unto them, Wheresoever the body is, thither will the eagles be gathered together.
Ceccarelli, M. and M. Cigola (2001). Trends in the Drawing of Mechanisms Since the Early Middle Ages. Journal of Mechanical Engineering Science. 215.3: 269-289.
Herrad, of Landsberg, Abbess of Hohenburg (1979). Hortus Deliciarum, ed. Rosalie Green. Warburg Institute: London.