Pregnant Cat ?: Feral

I take care of a stray/feral cat colony. "Quill" showed up around a month ago, off and on; now, for the past three to four weeks, every day. Starving. Enhales food. Gains weight, slight bulge on side. Disappears for two days. Comes back again today, still hungry, NOT noticeably thinner.
She is way too feral for me to pick up to see any nipples or feel her stomach. Is there any other way I can tell if she is pregnant and/or had kittens?
The location where she MAY have delivered is largely inaccessible and vegetation is thorny.
On top of this, I'd planned on TNRing her and some other cats this Thursday. How long can the mother cat be away from her kittens? If I learn at the vets that she recently delivered, I'd postpone spaying, and take her right back home.
Thanks.

She is most likely pregnant, but I doubt she's given birth already. Usually you can see the "deflation" easily (unless it was a very small litter). Plus most outdoor cats get pregnant between January and March (around here anyway; might be a little different down near DC), so it's a bit early for birthing right now.

I'd go ahead with the TNR plans, if the vet says she's nursing you can decide then what to do. I know that many cats who have a c-section are spayed at the same time, and most still nurse their babies, so maybe you could still have her spayed even if she did give birth. Best to ask the vet.

Thanks. I'll give the vets a "heads up".
I've heard the tail-tell signs of cats in heat around here for the past two weeks.
Among the cats in the stray/feral cat colony I am taking care of are three kittens, born around this time last year.

I bet she is pregnant and if you trap her Thursday, the vet will know immediatly if she has given birth or not yet. Hopefully not, of course..... Bless you for caring for all of these cats, you are saving lives

I was unable to trap "Quill", the Calico cat I think/thought was pregnant.
But I did trap a young, light brown tabby, only seen her once or twice before, who WAS pregnant.
Total trapped: two males, two females, and zero future kittens. Yeah !
May try to trap Quill the end of March, when I have an appointment with a low cost SNV place.

WOW Good for you and I think you are just great helping these cats and stopping them from breeding and bringing more feral kittens into a life of pain and suffering You are saving lives . for trapping Quill at the end of March!!!