There is no one answer for this question. I will show you a few theories that I am aware of that describe who this woman is.
Mary the Mother of Jesus
Considering who the child she bore is, it would seem to be Mary the mother of Jesus. The description from the above chapter matches the description from the Gospels about the events surrounding the birth of Jesus. The dragon is synonymous with Herod the Great, or even Satan who may have inspired Herod the Great. Herod attempted to kill the child, but God sent an angel to warn Mary's husband Joseph about Herod's plot, causing the family to flee to Egypt. This could be synonymous with the woman fleeing to the wilderness.
Some issues with this is that Jesus went with Mary and Joseph to Egypt and does not appear to have been "caught up unto God and to His throne." Also, the description of the woman in verse 1 is difficult to attribute to Mary.
Virgo the Constellation
Another theory, which is/was quite popular recently, is that the woman is the constellation Virgo and that a lot of this is about the stars and planets. Most people who support this theory say that the prophecy in Revelation is of not just one event, but at least two, the first one being the birth of Christ as I described above. Considering this and that Mary was a virgin, it is believed that the woman is Virgo because Virgo means Virgin. This sign in heaven involves the sun being in a place that is in front of Virgo (which happens every September/October), the moon being near the feet of Virgo (where exactly is under her feet has always confused me, yet could happen each month), and Virgo having 12 stars near her head (possibly forming a ring above her head, in my opinion). When she was pregnant, the planet Jupiter (the king planet) passed through her in a way that made it look like Virgo was giving birth to Jupiter. This is an interesting idea: the Virgin constellation giving birth to the King planet. Verse 5 gives some support to this. The crown of 12 stars upon her head is currently believed to be the constellation Leo (which has 9 stars as part of its outline) and the 3 planets Mercury, Mars and Venus.
This "crown" being present is what makes the September 23, 2017 occurrence of these signs unique. Every year, Virgo is clothed in the sun, every month the moon is at her feet, and every 12 years Jupiter moves through Virgo. For only a few days each year does Virgo have the moon at her feet and is clothed in the sun. Often times, Jupiter is in Virgo when this happens. But on September 23rd 2017 she also had a crown. The main issue with this is that there are more visible stars than just 9. Some have counted even 13 in a light-polluted neighborhood. Also, this is rather far above Virgo's head to be a crown; I would expect a crown to be a lot closer to her head. This combination of events is rare, but not unique to 2017.
Summary
We can speculate all we want, but we really have no idea who she is.