In Chapter 7, Myrtle isn't running away; she's running out to "a big yellow car", a "death car", and becomes the victim of a hit-and-run accident. Myrtle thinks the driver is Tom, who has just stopped for gas at George's gas station. George, Myrtle's husband, assumes Gatsby is the driver of the car, and Gatsby is willing to take the blame himself for Daisy.
In Chapter 8, George remembers warning Myrtle that "God sees everything" after he makes the comment that "God knows what you've been doing". He knows about Myrtle's affair with Tom Buchanan, Daisy's husband, and is planning to take Myrtle away, perhaps somewhere in the West.
Myrtle is another of Tom's victims as he uses her for his own selfish needs and then hitting her just for bringing up Daisy's name.