I have a 14 year old Female cat who just lost her Brother. She got along with him fine for 14 years.
She is not friendly at all with other animals. She hisses at every other animal. I want to get another cat from the shelter. I am looking at a 3 year old Male cat it seems very friendly. What should I do.

Why would you bring in another cat when you know your 14 year old female doesn't like other animals? Don't make her remaining years miserable. Let her live the rest of her life in peace and get another cat after she's gone.

I would think of both of the cats - it's not fair to either of them.Your Female doesn't have that much longer left to live. Why stress her out?

The process may take to 3-12 months. pets question and answers,www.5d2d.com

1. When first getting your cat to not let your intial cat meet with the newcomer.
(Your cat will smell the new stench)
2. After a week make the first encounter. Show your new cat to your old cat. Then leave then room and settle down your old cat.
3. Do this more and more each day for alonger period of time. (make sure you are holding the new cat).
4. Put a barrier between them so they can see and smell eachother but cant touch. They will eventually get used to eachother.
4. After you feel your old cat feels calm enough let your new cat free in the same room without any barriers (if things get out of hand immediately remove one of the cats.
5. Using these methods andintroducing your cat to your other one they will eventually become friends.

Tips: At the beginningmake sure they dont use eachother stuff.(food water etc.)

Personal experience

At three years old, he is in the transition of kitten to adult. And that is at least a positive, since a kitten and a senior cat is not a great combination. It takes longer due to the energy differences. pets question and answers,www.5d2d.com

She will hiss at him if you decide to adopt him. But I am not sure what you mean that she hisses at other animals. If they are just moving through the area, then it is territorial, and she is making sure they don't challenge her status.

When you bring a cat into your home that is not going away, hissing loses its effectiveness after awhile. She hisses, but he doesn't go away. Sooner or later, and accommodation will be made, and a new pecking order will be established.

But you also need to give her attention, so she doesn't feel neglected with a new cat around.

And also realize that she will be missing her friend of 14 years, so she needs some extra attention from that. As his scent fades, her concerns about her missing friend will also fade.

Is there another option? Yes. You can consider adopting two cats of similar age. They will focus on each other, and allow her to adjust. This can work.