hi

i recently bought a new kitten a couple of days ago she is 9 weeks old and i also have another older kitten who is 6 months, when i first introduced them i would of thought that my older kitten would be the problem but the new addition does not like him one bit, she hisses, growls and swats at him. i do keep her in a pen with supervision when let out as she is quite small compared to my big boy and he tends to be very rough, what i would like is some tips on introducing and also will she be more friendly as she gets older?

thanks