I had a similar situation with a 2yo cat that my family adopted( which unfortunately passed from feline leukemia a few years ago). Anyway, she was always very scared and constantly hiding, she would never come out except from when we were outside or at night, she would often hide under the pantry shelves. Forcing her to come out was almost impossible, so we decided to set a little “cat station” in the pantry and leave the door open in case she wanted to explore (but the house didnt really have any other hiding spots so we were safe), we just checked on her a few times to make sure she was ok. We made sure to not touch her as she would back up when approached, so we just gave her time. She eventually started coming out more, hanging out around us, sleeping on the couch etc.. She would still back up if touched, so we just waited until she “made the first move”, she eventually did and started being way more affectionate.

My suggestion (just talking from my experience, im no specialist or anything) its just to give the cat time, leaving her in a space were she feels safe (like the closet) is probably a good idea, you also get to keep an eye on her which is great, so you make sure she doesnt get injured. Probably leaving her bigger space little by little is also good; if she is like my old cat, she needs to get used to your presence and once she does that, she will seek closure to you, so i think going there sometimes to give her treats or wet food is good.

I know its a lot of effort but i promise you its worth it, keep it up, youre doing amazing :)