Mary,

Once the cat is in the trap, providing you have a cage for it to go in (which would be wise, as they are fairly inexpensive), just put the trap into the cage door and open the door to the trap. I can guarantee you she'll go in. Make sure you have fresh water, a litterbox, food and, and if there's enough room, a small box lined with plastic and old towels (in case she IS pregnant). Then just leave her be. She's going to be scared, but if you put a nightlight and radio with classical music. Give her time to calm down and get acclamated. Do you have a spare room to put her in away from your cats??? If so, that would be best. After about 48 hours, go and sit in the room and talk softly to her her, slowly blinking your eyes to let her know everything is okay. If she comes up to you in the cage and wants to be petted, then she's not feral, she is obviously someone's pet (yours????? ). Keep me posted.