Charlie and his sister came to live with us 4 and a half years ago, Poppy is much more outgoing, I wanted another cat so we rescued Wordy, he was about a year when we brought him home, I thought Poppy would be good with him, but it was Charlie that welcomed him more.
Someone for him to play chasin with.
When we rescued Harry(RIP) last July, he was 5 months old, he was wary of us but good with the other cats, especially Charlie.
Patience and time really, I have friends who introduce kittens to their adult cats no bother, but others try and keep them separate I suppose it depends on your older cat.
She seems interested, and there will be hissing, I used a wedge to have the door open a crack so they could see each other.
Good luck, looking foward to some photos.
Nicky