Maylin came to us as a very spicy girl. Apparently she was friendly until the day she showed up at the shelter. And the longer she stayed the worse she got.
They handed her off to me to see if I could help bring her back around. It was decided that she was not a candidate for adoption and never would be. There was no place to release her so we just opened the kennel and let her decide what to do. She knows where the cat door is. She uses it. But she also loves living on the kitchen island.
If we're very very careful, she will let us pet her now. But not too much. And you have to go through the whole ritual of getting permission first.
For certain cats, shelters do more harm than good, unfortunately. One of mine was a stray and we went through the formal process of taking her to the local shelter (pound) to confirm she didn't have an owner and get her checked out, etc., stating that we clearly wanted to adopt her if she had no owner. She went backward in the shelter (they flagged her as having "behavioural issues" - she initially started to warm to staff, but then became very withdrawn and defensive after they tried to wash her chin and stayed that way, apparently). She steadily recovered when we brought her home (no doubt being in a familiar place helped), although it took years for her to get used to strangers and her to stop responding to a couple of trauma triggers we were able to identify (I don't know what happened to her in her first few years of life).
To this day we're not sure whether they would have tried to adopt her out if we hadn't been so keen to take her. She has never been hostile towards us and her default is to run and hide if anything disturbs her (so on the rare occasion I get scratched if something startles her whilst she's on my lap or I'm holding her).
I wish you all the best with Maylin and hope that, with time, she'll improve.
Thank you for your service.