Need to catch a possibly ill older kitten/young adult. Are these good ideas?

I have a little feral colony consisting of four cats, one of whom just popped up recently.  Now I'd been giving serious thought to getting the three adults TNRed, I'm new to all this and feel way out of my depth, but this fourth one may be in urgent need of veterinary care, so I need to figure out how to capture her first.  She (I think it's a girl) is on the young side, seemingly not yet mature but not what you typically think of as a kitten.  She resembles a miniature cat at this point.  Something is terribly wrong with her right eye.  I thought it was missing at first because the eyelids are almost completely closed and what I can see of her eyeball looks dark and cloudy.  Otherwise, she seems healthy and spry.  I didn't note any discharge, which I think I would've seen on her mostly white face, so maybe it's not infected...?  I tried googling, the stuff of hypochondriac nightmares, I know, and now I'm wondering if something traumatic may have happened to the eye.  I'm just really hoping it isn't something like FeLV or eye cancer.  That isn't likely, is it?  She is such a little dearheart and I get a good vibe from her, even though she's too skittish to approach me just yet.  Her behavior reminds me of how my second kitty, rescued at 5 mos., acted when I first brought her home.  She displays interest in making a connection, her body language is cordial, she's fascinated by the sight of my kitties through the glass door.  She just lacks confidence.  I feel confident that I could get her socialized in no time at all.  And this one really, really, really deserves a good home.  

Sorry for the digression!  So, anyway, I'm new to the concept of trapping ferals and have been asking cat people I know for advice.  So far I've been told that I should try to ascertain when her meal times are, so I'll know when to set the trap.  One friend gave me great advice (maybe?!).  She said I should get either a trail camera or a baby monitor (with video, of course) and literally keep an eye on the feral situation, take notes on feeding times, that it would make TNRing everyone much easier.  Please don't think I'm crazy... ...I went ahead and bought the baby monitor.  If I contact a local rescue, will they loan me a trap?  if the little girl visits the same time other kitties are there, how do I manage to catch only her?  I've seen her alone and sharing a food bowl with the big boy of the clan.  And now I have another worry...  What if she's pregnant?  I was hoping to get her spayed immediately.  When do females begin ovulating??  Can I work with a rescue org. to get her medical expenses taken care of?  Or maybe partially covered?

I'm kind of a nervous wreck about this!  I really want to get this little girl medical attention ASAP.

Thank you for taking care of this community cat colony; that's really kind of you.
A couple of thoughts, in no particular order
I would keep feeding all the cats as the same time as you've been feeding them; the young cat should catch on pretty quickly. Yes, some rescue groups will loan you a trap(s). Ask them if they have any drop traps, too. You may have to put down a refundable deposit.
It's kind of hard to trap just one among other cats. You could try using a drop trap. What I've done is stay out by the colony when I am feeding them, and shoo away the cat I don't want to eat, the theory being, she'll be hungry when I set out the trap and the cats who have just eaten, won't be. Sometimes this works, sometimes now.
Regarding whether the new cat is pregnant: assuming female, probably, Then too, it is possible her eye is wounded because she got into a fight with a male cat. If she is healthy enough to be spayed (and over two pounds), then spay will of course abort the fetuses. When you take her to the vets, the vet will be able to make this determination.
Since none of them have been TNRd, I'd try to borrow as many traps as possible and TNR what ever cats you can trap. The same rescue group may be associated with low cost spay/neuter clinics or know of one nearby. Unfortunately, it is doubtful that the rescue group will pay for other type of medical care. You could ask them if they would do so if you are willing to foster the cat until she is ready for adoption. (Unlikely but never hurts to ask).
Good luck, and keep us posted.

Thanks for the informative response!  I don't personally know anyone who works with a rescue, but I know people who know people, and I see now that it's one thing to be unaffiliated with a rescue and borrow their equipment, another thing entirely to offer to assist them with TNR.  I guess I have to be a member to reap the benefits, so to speak.  Well, someday.  Someday.  It looks like the best thing for all involved is to contact a local group and let them orchestrate the TNR and do what I can to help.  I can't afford to pay for four surgeries and any incidental expenses.  A donation is the best I can do.  

I have a friend willing to loan me her trap (she gets so many ferals, it was worth her while to buy her own. Can you imagine?!)  (Wait, I forgot where I was for a second  )  I'm still bound and determined to catch the little girl myself and pop over to our vet.  If she's a good fit with the household, I may just keep her.  You know how you see a feral and instantly fall in a love a little?       I think I've got a cat crush!