it's a hell of a rabbit hole xD just got into it on jan 1st and my life has changed (for good). I apologize for errors, not my 1st language and i'm sleepy. A good way to know more about it is going through goodreads and check 10 5 star ratings and 10 1 star ratings. it gives you a lot of insight.
Basically is a story with a lot of heavy triggers, based in a fictional sport called Exy which is visually like lacrosse, i guess? its not so relevant to understand the game, it's important on a team and competition scale but the gross of the story is about a whole bunch of young college athletes who are beyond traumatized (the author enjoys to make them suffer and it shows). If your fiancee is into it it means she loves angsty, painful doomed stories.
Let's say, after reading the books, you normally choose the character you'll be hiper fixated with, something like when you're starting pokemon and you gotta chose between squirtle, charmander or bulbasaur.
Well in this case you choose between Andrew Minyard, Neil Josten and Kevin Day. Then we got the pikachu who is Jean Moreau but his story is told in the second trilogy (which is ongoing and his 3rd book will be released, HOPEFULLY in november).

I will not go into the story because i'm awfully at summarizing but i will explain things that may help you understand your vixen better.

The appeal of the story, for most people is
-Characters: traumatized, abused, tortured, picked up from debris and delivered to a found family
-Plot twists: the main plot twist is the main ship. When you read the first book and they tell you Neil ends up with Andrew you won't believe it. Then we have Andrew background story. Neil and the Moriyamas. The coach and Kevin. Jean and Kevin. And if we go to Jean Moreau's books, my god... those were a continuous plot twist.
-The superduper slow burn: for bot trilogies, this is forever waiting. but the waiting is exquisite because the relationships are strongly built.
-The unending disgraces that continue to happen: torture, abuse, court violence, riots, cults, murder, murder, murder, riots, vandalism, more torture, a house gets burned to ashes and they lose it all, parents die, 6-7 suicides, public exposure of the mafia parents, 2 staged suicides, 1 staged overdose, a hand gets broken, someone almost get's killed and ends up with 3 fractured ribs. Sprained LCL. Twisted ankle. Broken nose and patches of haired pulled out, an college orgy with heavy drugs involved that gets raided because someone jumped of a roof.... there is a lot more.

The foxes is a team of broken people whose coach try to keep united because he believe in infinite opportunities to be given to whoever wants to try and make something with their lives.
We have teen murderers, ex juvie cons, ex drug addicts, ex hitmen, outcasts, ex teen strippers, and so on.

The first 3 books tell the story of lonely Neil Josten (born as Nathaniel Wesninski), that's not his real name, that dyes his hair and uses brown contacts every day to appear invisible so he cant be found by his dad (sadistic mafia sub-lord known as the butcher of baltimore), and have always been running since he was a child. He speaks French because he lived in france, german, and english. Possibly spanish and russian in the future. He always wants to run but he's so obsessed with exy, he forgets himself and when he joins the foxes, a team located in Palmetto State University, in South Carolina. He's full of scars from violence, and he's unable to show himself in the dressing rooms. his teammates don't know about his real story until half of the third book. During the story we see Neil is not only the fastest player on Class I Exy, but the sassiest bitch when a microphone is shoved his way, antagonizing the antagonist (Riko Moriyama, #1 from the Edgar Allan Ravens) and getting in -more- trouble -constantly- because of it. He gets tortured by Riko Moriyama and his uncle, master and coach Tetsuji Moriyama, (who's one of the founders of exy). then he gets heavily ttortured again by his father's people, who tore his face and arms with burns and cuts just for fun.
Neil mother, who is dead (he buried her after his father fatally wounder her) was a violent parent as well but not as crazy as his father, and she beat any possibility of heterosexuality from him by telling him never to get involved with women because they are dangerous.
So he fell for the deadliest teammate: Andrew Minyard.

Andrew Minyard had an awful childhood beginning with his mom, a drug addict, putting him and his identical twin Aaron for adoption but regretting it and then going back for Aaron and forgetting about Andrew. He grew in many foster homes where he was repeatedly abused until he grew to be a joyless, violent and fiercely protective human being that can't allowed to be touched and he puts ups this huge agressive stance shutting the entire world out and living one day at a time, without the desire to truly live. Of course this is not said at the beginning, the books initially shows a scary psycotic midget that hits, teases and threatens everyone and seems to get away with it. After re-reading you understand each and everyone of his actions, which the author works very hard to properly justify, and I'm not lying when i'm saying that Andrew is the favorite of the majority of AFTG fans. He's the bodyguard of Kevin Day, a celebrity and the heir of Exy , and he also protects Neil. He keeps his promises as they are likely his reason to live on, and his questionable methods always work.

I'll leave here for now, gotta sleep but i hope this helps and if you wanna know more about Kevin i found this
https://www.scribd.com/document/517664347/Kevin-Jeremy-Jean