Feral mom, what is best? Help!

Ok, I have another feral mom that is ready to give birth at any moment. Here are some facts:
1. She lives on the roof of the parking garage.
2. The garage is in Metro Phoenix, and it will be 93 or so today
3. She has never let me touch her. She usually walks (she doesn't run) if I get too close but for the past few days she's just been hissing because she's too pregnant to run.
4. I have a cat in the house and no "spare" room I could keep her and the kittens in.
So, here is my question. Is it more humane to leave her here and let her do what comes naturally? Or should I try to trap her and take her home and put her in a cage in the backyard? Either way, she'll be raising kids in the heat.

I have already called the organization that took the 5 orphans I had last weekand they have no openings and in fact told me that in Maricopa County, 800 cats/kittens are being euthanised each month.

Any advise? I put out a box with a blanket in it last night hoping that she would find that comfortable, but she's still hunkered down under a car.

PS> the organization is helping me to get a TNR going for the colony here.

im sorry i dont have any advise , but if you post this thread in the feral section , or the cat sos you may get a quicker response. and a bit more help. good luck.

Do you have a cat run/ cage in the back yard? I think it's best to trap her, as if she gives birth and raises the kittens up there on the roof, the kittens have no way of getting food or water or getting down. Also, they will be very hard to trap once they can run. Start ringing around now, friends, family, shelters, SPCA, cat rescue leagues etc. I'm pretty sure there will be someone willing to foster her. Heck, if I was there, I would take her.