The thing is, her face works well for her personality and I was used to the way she looked, so I did not want to wholly re-invent her. Just being prettier wasn't the point, she needed to still be Piper. So there was no supermodel treatment, or slathering on makeup and fancy hairstyles. Rather, I sought to emphasize her attractive qualities and re-shape others with a touch here and a tweak there; no changing her basic facial proportions, adversely affecting her facial expressions, or removing any features that I felt made Piper look like Piper. After many revisions I came to a result that, I feel, is still the good ole' Piper that we know and love -- just with an extra couple doses of heart-throb.
It should be noted that, in my screenshots, I am currently using Valkyr's face textures and deLuxe's lip liner mask (and ENB in some), so she will look a bit different if you don't have those. However, this face does not require any other mods such as eyes or hair.
v2
I updated Piper slightly with changes to her nose and forehead, which both makes her look better and brings her face closer to the original.
Now she is an even prettier and even Piper-y-er Piper!
Installation
Mod Manager: Download with your mod manager and enable.
Make sure .esp is checked, and that you do not have other plugins that edit the NPC loaded afterwards.
If you would like to use this face with another mod that alters Piper, you can use Face Ripper (URL below) to import this face into the other .esp. Simply choose this .esp as the source, the other mod as the target, and make sure that Piper is selected in both pull-down boxes.
Thanks
At this point I must credit xatmos and his brilliant Face Ripper application, without which this mod, or really any modifications to NPC faces, wouldn't be possible -- at least not without extreme inconvenience. Also, the crew responsible for FO4Edit, which I used to extract Piper's original face in .esp form. Amazing tool that enables nearly every mod on the Nexus.