I can only tell you what has worked for me. I have 11 who were/are semi-feral at the moment. Some have been here since 2001 and are still not real friendly.

Borrow a large cage. Put it where the action is. Provide food, water and a litter box. If the cat seems to be freaking out, cover the cage with a sheet for a few days. Keep the noise level down as much as you can too. After the cat seems to be less upset, remove the sheet. Talk to the cat a lot, using a quiet voice. If you can, pet the cat several times a day. Eventually the cat will accept the petting and possible even want more. How long to keep the cat in the cage will vary with the cat's acceptance of you.

If the cat is not a complete, freaking feral, confine it to a room with the food, water and litter box. Visit often, bringing tidbits of food and a lot of quiet talk. Read or watch TV in the room with the cat. Let the cat come to you when it's ready. When you think it's time to integrate the family, install a screen door to the room so the animals can smell each other. Or only allow one of the other pets into the room at a time. There will be squalling and hissing at first. Hopefully no serious cat fights. When everyone has met and seem to tolerate each other, open the door and walk away. The new cat needs to be able to come out on her terms.

It has taken up to 4 years for some of mine to feel comfortable enough to come out of the cat room when I'm there. Some didn't wait a day.

It takes a lot of patience.
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Xena sounds like my cat, Shai. She was (and is) a spitfire. I thought for 3 years that she was still afraid of me. I sent her picture to the pet communicator and discovered she wasn't afraid of ANYTHING. In fact she was insulted that I thought that. I apologized and she immediately became more friendly. But on HER terms, of course. She came out of the room quickly but wouldn't let me touch her before. Now she will sit on my lap (when she chooses to) and sleep with me, a dog and another cat part of the night. And this happened within 3 weeks of my apology!

Please keep us updated on what method you use and how well it works.....or doesn't. You might get lucky and have her sitting with you in a few days.