My kitty Arcadia

In June 2015, I was at Eat n Park (restaurant in PA). This girl comes in all frantic and says whoever has the white PT Cruiser, there was a note on their window that said a kitten was stuck in the hood of their car and they hear meowing. It was my car. I went over and thought they were all nuts bc I just drove 45min from work and never heard of cats going in cars like that before then. After about an hour, we manage to get the 8wk old kitten out of the hood of my car. I take her home, get her to the vet the next day and care for her. Her fleas were embedded in her skin under the mats of fur this poor malnourished kitten had. Unfortunately, we had to shave her and then bathe her in dawn dish soap but it worked. I got her shots and kept her. At first I kept her in the bathroom (big bathroom) and would go in and pet her and tried to get her used to people. Once I got her shots and stuff, I got the okay to let her around my other cat. People said to leave her alone that she would come around. A few months goes by and it was still like I only had one cat bc she was in hiding except to eat. Then I tried finding her and socializing her again. Nothing. Recently, she will come out and let only me pet her in the morning or when I'm going to the bathroom lol. And only if my son is asleep or not home. If I try to approach her, she darts like I'm going to hurt her or something. She doesn't clean herself. My other cat occasionally cleans her. She's not vocal. Once in a while she leaves out these tiny meows that sound like a little bird chirp. She's only purred one time that I've heard her recently. She was in the hallway the other day and my fiancé bent down to pet her and she bit him good causing a blood infection that landed him in the hospital. I keep getting the same advice, to not give up and keep trying. I am. But is there anything else I can do other than leave her alone? I feel like she's miserable. Maybe she's just a weird cat. Idk. Also, is there any way to clean her mouth bc I'm scared if my boy tries to approach her, she will act in fear and bite him too. Anyway, that's my story.

I don't know who told you to leave her alone when she was little, because with cats, the younger they are the easier they are to tame.
Up until recently I have never had a full time cat, I've been strictly a rescuer and foster mom. I have had so many feral babies under 8 weeks old, and every single one was given a day to settle in, then comes me forcing the love on them.
It sounds terrible, but if a cat is feral they have to have CONSTANT reminders that people are good, people give pats, people give me food.

Since your kitty is older, but not old of course, you still have a good chance at socializing her, but it might take a lot of time and patience.

I would go back to keeping her in a room by herself for now, go in periodically and sit in the floor. Don't go to her, let her come to you. The room shouldn't have an excess of hiding spots, and all her necessities should be in there. Have treats, maybe some good wet food that she doesn't get very often and let her eat it beside you while you're in the floor.
Really the goal is to prove you're not threatening, and you're not trying to catch her. The first step is earning her full and complete trust, then the rest follows.
While you're in the room with her make sure you're talking sweet to her, have a string toy that you can play with her from a distance with. Haha you have to make your friendship worth it to her!

Best wishes and keep us updated, I hope that helped some.

Ditto the above.  I would recommend that your boyfriend and son also spend some time with her.  (supervised if your son is young).

Same rules apply - get down on her level, don't push her.  Reading out loud is a great way to get her used to your voice and your presence.

Allow her to reign her own space for a bit.  It will give her some confidence.

We have a cat with no voice, too.  She was starving and parasite-ridden, too, and apparently it did some damage to her ears and voice.  She squeaks rather than meows.

A vet visit can help with her teeth - she may need dental work.  Cat bites of any type can be nasty, so it won't hurt to check.

Thank you for hanging in there with her.  It sounds like she needs you!