Some cats are just like that - especially FEMALE cats...
This very thing happened when I moved in to Lucy's house with Mishka. She is just so mean to him. She
growls, hisses and whacks him every chance she gets. And he doesn't give up but also - he gives it back to her.
Sometimes we hear them in a fight and it's just scary - they both scream bloody murder!
Fortunately I don't think it's has ever gotten too serious - no claws or teeth that is. We have accepted that they will never be friends. Now having said all that - we have noticed lately that they are ALWAYS in the same room together. Not cuddling or anything like that by all means though!!! It has taken them 4 months though!!
They do seem to be getting along better - that is that Lucy The Bitchy Tabby may be finally softening up. If it was up to Mishka they would have been friends a long time ago. Once I saw him trying to climb in next to her to lay down and cuddle - for the first few seconds she just looked at him in disbelief and almost looked like she might let him - but the of course he got a good whacking on the head and scampered off...poor guy!
So what I am saying (in a very long-winded way) is be patient but just accept the fact they they may never be cuddle buddies!