Feline URI's, calcium oxalate and surgery options

Any help or advice is appreciated.

Background:

My sweet 7 1/2 year old female cat Aggie is on her third bout of URI's. The
first was treated with a basic antibiotic; the second last January was
treated with trimethoprim sulpha (nasty e coli bug); she was clean for 5
months, now another e coli bug is back (her tests were done with sterile
needle to get the samples). We're now waiting for the extended panel from
Cornell to come back and let us know how to treat this one (the last one had
few antibiotics that would work, and the trimethoprim was the only option
that didn't require hospitalization).

She also has chronic kidney disease, but no clinical signs, and her
bloodwork shows only very mild elevations. She's on k/d for her diet with
distilled water, which should according to my vet be a good diet for her,
because she shows on x-rays and ultrasounds to have kidney stones as well as
bladder stones and sediment. The crystals in her urine are calcium oxalate.

Here's the questions I'd appreciate a second opinion on:

My vet says we must kill these nasty infections (of course). However, the
last one could have killed her, it was rare and only susceptible to 3 or so
drugs (all somewhat toxic to her kidneys), so we got lucky that she
responded well to treatment at that time. God knows what the extended panel
will say about her current urinary tract infection when we get it back
(probably Monday). She's straining, I've seen blood droplets in her box,
and was throwing up every few days lately. Hopefully, we'll again find a
good drug to stop all this. However, this is starting to feel like Russian
Roulette. Which leads to:

My vet says there's no guarantees that surgery will do anything to cure her
of these infections or recurrence of stones. But we never saw URI problems
until age 6...so why not take the risk and clean that bladder out? We can
be careful to hydrate her, etc. during surgery to avoid kidney problems.
Otherwise, if we don't do surgery, it feels like we're just waiting on the
day that a nasty URI will appear that CAN'T be killed, and then...

What really are my options and her prognosis, given all this? Any informed
opinions are welcome.

Thanks so much,
Setch