The second girl (andf third) is using scale armor, but the first one isn't. I haven't seen any real scales that look like that as of yet. ^^; Whatever the case, tackle the scales first. For the amount of time and effort you'd have to go through to make reinforced foam scales, you might as well do the real thing - which isn't difficult so much as it is time-consuming. Scale armor is actually very easy to craft - much easier than if she was wearing chain mail, that's for sure. ^^;
is a great tutorial you can follow to do a scale top like the second girl did.
As for everything else... all official artwork I've seen of Lady Loki isn't really consistent. Something is always
changing, so you actually have a lot of leeway as to how you can handle it. Green body suit, black body suit... Greean and black body suit, fitted pants and low cut shirt or whatever... There are lots of options. though most tend to settle for the green unitard look. However, the only thing really consistent is the drape and belts in front, and the fact that she does have scale armor. More often than not, however, her outfit is cleavage bearing (what kind of super villainess would she be if she wasn't showing off the goods?). So again, you have lots of freedom to experiment on what will actually be underneath the drape and armor - so you should decide for yourself what would look best on you, how to make yours unique, as well as what will work better for whatever budget you have.
Now the horns... OTL the horns. Even I don't know how to go about those - which is probably why I'm handling them last when I go through with my Lady Loki. One girl I met who had an awesome lady Loki told me she cut up some of the oversized candy cane christmas decorations and worked from there - which is a great way to have symmetrical horns, but they're not quite the right shape I think.