Pregnant feral cat.

My friend has a feral cat in her community that has 2-3 litters a year and they always end up in her garage. There is a cat door on the garage door for her own cat, but "Belle" will move her kittens there when they are old enough to start eating food.
We know that the kittens are in the garage (hidden very well) when the resident cat refuses to eat in there.
We saw Belle last week and she was huge, ready to deliver any day. Saw her again today and she is thin. Not sure where the kittens are right now, but know they will be around soon.
The question...how to catch a feral cat and have it spayed.
I know we could get a humane trap, however she is a nasty cat and would freak out if we tried to take her to the vet. I am not even sure they would be able to sedate her in order to get her out of the trap.
Any suggestions or comments would be greatly appreciated. We have taken in 6 litters in the last 2 years and it is getting increasingly harder each time to find homes for the kittens, not to mention it is getting more difficult to work with the feral kittens and socialize them.
Thanks for your help!

If you can tempt her into a humane trap/cage...tempting her with food, once she is in the trap, quickly put a towel or sheet over the trap/cage. Being feral, she won't freak-out as much being trapped. Once she is at the vet., he or she should know exactly how to handle her.

That's very nice of you to want to get involved in doing what is best for this mother cat & her kittens

Trapping her and taking her to the vet is the best thing and yes cover the trap, they seem to settle down when you cover them, I trapped 11 cats last year 6 that were female, I took all to the vet and had them taken care of, I now have 5 almost 4 month old kittens that I trapped and got mommy also, she wasn't bad at all though, she was pregrant again when I got her to the vet also, had her all taken care of and on the 12th of july I will start with the babies to the vet witch are all females,these babies are quit the sweethearts though as I have had them at home for about 5 weeks or so, The vets know how to deal with them, as long as they know they are feral, I dread to think how many more there would have been next year had I not gotten 12 females taken care of, good luck and keep us updated

you are doing a good thing. i agree with covering the cage, and that the vet will know what to do. Keep up the great work