When or if its right to bring a new cat/kitten into the home after a loss.

Question
I adopted two stray kittens 3-4 years ago. Then another one found me two years ago. The first two were siblings and got along well. The male (Numark) was more dominant. For example, i would wake up to him haved mounted his sister (Boo), and her making a some noise. All of my babies are fixed. I stopped them every time i caught them, and she never really fought back. Also, Numark was very possesive of me, he would headbutt any cat that wanted attention from me while he was around me (which he was always). Anyone could pet Numark if they pet the other cats first. He couldn't stand them getting attention without him getting some also. It was mainly Sully (my third addition) who allowed anyone to pet him. Sully is extremely friendly with everyone.
    
   Boo never completely warmed up to Sully completely. The three would all sleep in a 'pile' together, but Boo never really wanted much to do with him.
   
    I guess now would be a good time to explain where i'm going with this. Numark died unexpectedly in the move into a my new apartment. He was in the carrier with Boo, his sister, when he died. There were no indications he would leave me, he was very healthy and athletic. This was terrifying and horribly upsetting to me. I can't imagine what Boo felt and how she's dealt with it. She has always been VERY timid of people, even of me at times. She runs away at the drop of a feather. She does become very affectionate with me and a few other people she knows well at times. But she still isn't very friendly with sully, and it's been about 4 months since Numark passed. She doesn't hiss or swat at Sully, but he does chase her often and she ALWAYS assumes the defensive position when he does chase her down. She's very submissive and timid. I have introduced her to a new cat in the past. A new roomate moved in with me last July, and he had a large male cat. She chased him down and was a huge annoyance to him, Always following him around and such. Even after a slooow introduction and almost 6 months she still hadn't warmed up to him.
   
    I took her in when she was about 5 weeks old, and she was on her way to becoming a feral cat if i hadn't taken her and her brother in. I guess Numark just attached himself to me and trusted whatever choices i made. I miss him dearly and would love to bring a new addition into my house. Sully will be fine, he's a sweet, very affectionate, very trusting little guy, but i'm afraid Boo will not adjust and end up even more of a recluse. I was wondering if there was any way of working with her, and if a male or female cat/kitten would be better. I just wish she could talk to me and let me know how she's doing, and what i could do to make her feel more comfortable as a whole. I've been around cats my entire life and i'm at a complete loss with this. I want her to have a companion like numark, but i don't know if she'll ever adjust to or like any new addition. I just want her to be happy.
Any information would be very much appreciated. If you have any questions, feel free to ask.
Thanks,
Sue


Answer
ok to my knowledge u have a male and a female cat....if you want to get another cat getting another female would be best because of territorial purposes.  The only way it would be easiest to introduce a new cat is if its a kitten and just let nature take its course and see how they interact.