I feel like you could focus less on how badass and hyper violent she is, and make her more relatable. As it is, you explicitly put it out there that Ghost kills most people she meets - and then wondered why you weren't finding any lasting character relationships.
You don't need to be a nice or good person to have friends, but you do need to have more to you than 'a killer who kills a lot and is really good at killing'. And you also need to find threads and ways to interact with people that aren't also just violence - the fact that when someone says to thread and find stuff that way, your reaction is 'skirmishes' is kind of tell-tale - you're a military person, okay, that is understandable.
But the military isn't fighting 25/8, they have time to relax, to recover, most people in the military make friends with their fellows, they go to bars and hang out and basically act human. If you only focus on the fighting aspect of the character, obviously the personality and relationship aspect will suffer.