She may be too little to set off the trap. I’ve done this with the ferals that have shown up at the various properties I’ve lived at: I just sat on the porch far away at first, then inching closer and closer as they became more comfortable. Sometimes if they were jumpy I would wait til their backs were turned and grab them. I’d rather grab them than throw a towel over them as they could get out from under the towel before I could get a secure hold. After they figured I wasn’t out to harm them and would in fact, get their faces stuffed even more, they were ok.
I hope you can get your hands on her soon. My feeling is that even though you are feeding her, she may not be getting enough nutrition to catch up from the days she was not eating. Kittens burn incredible amounts of calories just growing.
Is there any way you could set up the trap so that you spring it and not her in case she is too light to set it off?