5 year old adopted cat TERRIFIED… is it a mental problem?

I recently adopted a 5 year old persian cat… her name is Adele… the previous owner moved apartments and said that he was unable to bring her (ridiculous excuse), so he gave her to our vet (we go to the same vet) the vet told me that she stayed with her for about a week and she would HIDE into tiny corners and would not come out for 2-3 days until she was STARVING… shes super skinny now. The vet works full time and cant really give her the attention she needs, so she offered me Adele, knowing that I own 2 other persians and 3 calicos. Now the vets story was, Adele turned out to be pregnant when she was adopted by her, and when she gave birth she just ended up stepping all over her babies, not caring… none of them survived ( Adeles former owner had 3 other male cats, she was the only female… supposedly she was constantly bullied by the male cats…and her owner worked at home full time, so could it also be seperation anxiety???)… Adele now stays in my spare bedroom, isolated from other pets, and I have given her a bed, a place to climb on and toys… I dont know how to explain it but she is emotionless… ive tried wiggling a toy in front of her and she wouldnt even look at it… her pupils are constantly dilated and EVERY TIME I enter the room, she goes and hides into a corner and then hisses at me. she would never bite or swipe at me… i have touched her before but even that she doesnt show any signs of pleasure even if I pet her in proper places that cats usually love….so i’ve refrained in petting her as she might not like it…. I’ve had her for 2 months and a half now and the only improvement shes had is that she eats regularly now and drinks a good amount of water… but other than that… she still hides, hisses and doesn’t play with anything. She seems very depressed/strssed out… will Adele get any better?
PS feliway is not available in my country at all 🙁 i live in the philippines