Well, I load in the figure for the BODY first. If there are several figures for the body, in this case there are. Than I load one of them (in this case I went with Ashlyn first). I then go to the shape tab and lower Ashyln to 50% and I experimented A LOT with many other characters until I tried FW Wanda HD. I then experimented with different combinations, different percentages of each, looking CLOSELY at different features, usually facial and how they change and modifying them until something feels right (or close enough). I actually tried a lot of different characters for this until I settled on Wanda.
The Skin is easy, just go to the People -> Genesis 8 Female -> Character and to the folder for that character and there is usually a Materials folder which has the skin, or sometimes it's right in the main character folder. Just double click the skin option and it will apply the skin without altering the body shape (you can do this to make your own unique characters, just pick a body shape you like, then try applying different skins to it).
I spend a ton of time just tracking these down, mainly her skin to find the various moles etc...and match them up. Then A LOT of experimentation with different body shapes and percentages as I said.
I will usually grab a ton of screenshots of the character in game or I will go to the game's image folder and copy everything for that character I can find, from different angles so I can use the angles to get the body shape right and check out the moles, eye colours etc.. etc... etc....