Aggressive cat? Please help.

Hi, I have a spayed, declawed, female DH cat, Tillie, who is around 2 years old and she is almost constantly growling and hissing. I feel sometimes she is giving me mixed signals as she loves for me to rub her cheeks, but will growl the whole time while showing body language that she likes it except for her tail, I tend to avoid petting her unless to comes up to me which is rare, but still she growls and I still don't quite understand why. Her history to me is unknown, but I'm starting to think something traumatic happened to her.. All I know is that the family I got her from who had small kids (3-4 yrs) and probably harassed her, as when I went to pick her; the mother was having to tell the kids to leave the cat alone, tell her she's fine and etc. They also had another cat that constantly bothered her, so she is pretty fearful of my kitten, but I nicely keep them separated until I properly have the time to try and re-introduce them or perhaps after I find the 'why' and/or 'cure' to her constant aggression. Though she has never actually bit me, it is more just growling and not stopping, she even hisses at herself when she is itching. I noticed that she is very sensitive to anything around her neck as one day I tried to put a harness on her and she turned more physically aggressive, so I backed off and never try to do something like that. I feel she is in pain, rather that be mentally or physically, I hate seeing her like this, please help me so I can help her. =,(

I am a human doctor, not a vet.  From the history above I suggest that you take Tilly to a vet for a check-up before you try to deal with her yourself.  Incidentally you have mentioned one particularly traumatic and frustrating experience when some vet declawed the poor cat -  but we should await the vet's report..

Can you let us know what the vet says?

With best wishes,

Geoffrey

I was not the original owner, hence why she is declawed, I feel so bad for her.. While my kitten still has all his wonderful claws.
I will try to schedule an appointment as soon as I can, but I've got very little time and very little money. It might be awhile but I sure will get to it!
Thank you so much.