I suspect this a model mesh issue and not a texture one, so I'd be inclined to think tweaking FemShep's neck mesh to better fit with the buff bodies mod would be simpler and less intrusive on the modder's work. I think this can be fixed without modding the actual buff bodies meshes, though. I'd like to request a fix for this, since it appears the original creator may not be available or inclined to work on it. The mod hasn't been updated in over two years, and it still has an issue: the neck seam is very visible whenever Shepard is in either her underwear mesh or the tank top outfit. The mod also has a casual outfit replacement mod to accompany it, which replaces FemShep's armored combat fatigues with a tank top that includes both clean and 'dirtied' textures for the opening sequence. Arguably this makes certain shared animations between herself and MaleShep more awkward (her arms look a touch weird during one particular shot at the Defense Committee meeting), but it also makes other scenes look more sensible (most notably whenever she's doing something physical with James Vega. It's called the Buff Female Shepard Body Mod, and its basic effect is to make FemShep's body appear more physically fit, in keeping with the idea that she's a marine who's gone through intense training. So there's a pretty cool, fairly subtle mod for Female Commander Shepard on Nexus that I quite like.

Mass effect 3 casual outfits female