I don't think I have all the answers but having spent the last 2 years catching over 50 cats in CDN, this is my best advice. Since a few people have asked me for advice, I'll post it here publicly. I know there are other "cat-snatchers" on board who have different tactics and ideas.
There is more than one way to catch a cat
This was my way:
The fastest and easiest way of trapping a feral cat is a live trap. Your local SPCA or rescue will lend one out to you.
If that's not an option, you need to have ALOT of patience. Unfortunately, my ferals went through a few pregnancies before I was able to trap them. But they were quite older and I was trying to tame them AND trap them at the same time. Today I know that it's much better to trap them first, tame them next in a more controlled environment.
A feral cat needs to depend on you for food. Regular feeding will associate you with food. A routine will calm a feral cat and build expectations which will eventually pave the way to a trusting relationship between the cat and you.
Start a routine with her. Always feed her at the same time, always call her the same way, always use the same pet carrier and always at the same place. Try not to move the pet carrier from the same spot. Call her and wait for her to show herself. Let her see you prepare her feeding. Prepare something that will surely get her inside that cage for the first few times. Nothing works better than hot rotisserie chicken or canned tuna. Change it to regular cat food once she's used to going in. Try to feed her everyday at the same time. Put the food at the end of a HUGE pet carrier and walk away. If she doesn't show up, don't leave the food behind. Feed her only when she shows up. For now it’s more important that she eats because of you instead of at the same time every day.
But eventually, you’ll manipulate the time you feed her so that it’s consistent.
Your goal is to get her to depend on you and associate you with food and to trust the pet carrier.
Continue the routine. But instead of leaving her alone with the pet carrier, settle nearby: close enough for her to see you, far enough for her to feel secure. Stick around until she starts to eat in front of you. If she's eating in front of you, she's beginning to trust you.
Your goal now is to get her to eat while you're nearby (a sign of trust) and closer to her while she's eating inside the pet carrier. Remember, if she doesn't show up, don't leave the food. If she shows up later, you can feed her later but with the same routine. Return to her regular feeding time right away.
Keep the same routine but instead of sitting at a distance, sit right next to the pet carrier. She needs to get into that cage to eat. All four paws need to be in and not only the front two. Your goal now is for her to eat while she's inside the pet carrier and your sitting next to it.
Phase IV: The TRAPPING
1. Make sure she's hungry. Instead of feeding her on time, feed her either the next day or later in the evening. ( Most people can't find the heart to skip a feeding but it works the best if you do).
2. Go through the movements of closing that cage door so that nothing goes wrong (i.e. the bottom metal of the lock sometimes will get stuck in the ground and the door won't close; the cage will flip flop on an unsteady ground making it difficult to close the door.) Practice the movement a few times while she's not there. Try to foresee any problems and solve them before you trap her.
Have her favorite food: Hot rotisserie chicken or Tuna from a can works the best.
Same routing. Call her, let her see you prepare the food. Put the food at the end of the cage. Sit next to the cage and wait.
If her back paws are out of the cage, don't close the door.
Leave it for the next day. All her paws need to be inside the cage. A trapped feral cat goes NUTS for the first few minutes. Be ready for it. If you’ve never seen it, it’ll make quite the impression on you. It's very frightening and her panic will scare you before you can ensure that the door is securely locked. If she runs out, the pet carrier will not longer be a safe place for her. So be sure she's inside completely and you can calmly close the door. (I wear gloves so that I'm not scratched while she's inside and I’m manipulating the lock on the cage).
How long will all this take?
I don’t know. Depends on the cat and how fast she will trust you enough to eat while you’re sitting nearby. It could take a few weeks, it could take a few months. You can never tell how fast she will progress. It depends on her past exposure to humans and her temperament.