Need trapping advice for trap-savvy cat...

I need some expert trapping advice. I am trying to catch Layla, a stray semi-feral cat...she has been trapped twice before (once for spaying, and a second time by accident while trying to trap another cat).
I need to trap her this time because Tuesday of next week she will be going to a foster home, and in December she will be going to a rescue that will socialize her and hopefully adopt her out eventually.
Her vet appointment to be FelV/FIV tested, vaccinated, and dewormed is this Saturday. So I do have a deadline.

I figured it would be more difficult to trap her a third time, so I got a trap tonight (Wednesday). I tied the door up and put food in the back of the trap for her...she wouldn't touch it. So I went out and put some food more towards the front of the trap (a few inches in) and she did end up eating that, but she still didn't touch the food in the back. Since that is where the catch plate is to release the door when I'm trying to trap her, I'm thinking it's going to be difficult to get her this time.

So I need suggestions. Anything will help...I have Thursday night and Friday night to try to catch her before her vet appointment, and if I can't catch her by then I'll have up till Sunday night to try to trap her.

I don't know what else to do. I tried covering the food end with a sheet, and she just ended up pulling it off to try to get to the food from the outside (or it might have blown off).

Thank you in advance for any suggestions you can give!

Try original recipe Kentucky Fried Chicken, deboned and deskinned. Drop a trail of small tidbits leading into the trap and have a larger portion inside the trap.

For some odd reasons, cats love the stuff.

Okay so even with all your great suggestions and advice, I didn't catch Layla in the trap tonight.

I caught her in a cat carrier! There was another stray cat that showed up all the sudden (I'm guessing it's the same cat that ate the food from the back of the trap last night, so he/she came back for more). Anyway, this cat was beating up on Layla to get to the trap, and I was getting frustrated by it. So while the other cat was busy with the trap, I brought out my large cat carrier and put tuna in the back of it and trailed some dry food in there. I kneeled beside the carrier and Layla got comfortable with me soon enough, and then I just waited until she finally got all the way inside and I slammed the cage door after her (had to slam it fast, I knew if I messed up once and she somehow got away, I'd never have a chance of catching her ever again).
Oh, I didn't end up catching the other cat...the trap I used is from the humane society, and it sucks! I set it so sensitively and this cat still didn't set it off. So I wouldn't have been able to catch Layla with it even if she was comfortable about going inside it.

Anyway, Layla's safe. She's spent her last night out on the streets, no more scrounging for food. (Glad I got her...it's freezing here! It's supposed to get down to 25 F tonight).


Heehee, she is not a happy camper. Poor thing.