(a) Create 'Duplicate Layer' as Background copy (destination original document).
(b) From Layers tab, right-click Background copy and select Blending Options and change Blend mode to Multiply.
Duplicate Merged Layers and go back to step (a) using original as destination three times.
Before spending time to xray a pic, I use a freeware app called AI Picture Explorer that does the same multiply thing quickly. Select Enhance, then Fix OverExposure, then UnEqualize.
The "region of interest" is her top. After multiplication, the hidden shadows will be visible but the image will be darkened somewhat. Use the Quick Selection tool of PS to "isolate" her top so you can blend the shadows with original as background layer.
As c-through likes to say, "keep it real".