Pressed her back is would to have her back right up against something. The word "simmered" is to describe the lights on the road, but personally I think maybe the word is incorrect. Simmer is when something is boiling at a medium pace and is often talked about when cooking. So to me, it doesnt describe the lights down the road well. Now I think the passage should read "shimmered" which means a visual image is moving around almost like in a wave type of shape. Lights on a road often would give that appearance. So "a few lights shimmered down the road" suddenly makes a lot more sense 😃.

A few lights simmered down the road simmer is less than boil, it is low-key, non violent, less noticable. Maybe metaphoric for that? . "pressed her back against X Stand with your back to X, in contact with X. Indicates standing close by, as close as you can get, usually to be unnoticed, or out of the way.