When hyperkalemia occurs in CRF cats, its usually because the cat is either
oliguric, over-supplemented with K, or in the terminal state of the disease.
Since your cat was initially hypokalemic, my guess is your vet
over-supplemented potassium (K) - since its unlikely your cat went from
hypokalemia to hyperkalemia that fast - hyperkalemia usually doesn't occur
that quickly.

If I were you, I'd speak to your vet about a diuretic (Furosemide).
Diuretics stimulate urinary output, which facilitates the excretion of
excessive K and renal toxins.  Furosemide should increase urine output
within 30 mins. If it doesn't, the dose should be doubled, and then tripled
at hourly intervals - although I don't think doses above 2 mg/lb are any
more effective.  That's, of course, only if your cat is oliguric.

The only advantages of dextrose over flurosemide is its cheaper, provides
some non-protein calories for energy and is readily detectable in the urine
when its effects begin.  However, there is a real risk of overhydration if
your cat severely oliguric. I think Furosemide is much safer and should
begin to work in about 30 mins.

The problem with potassium levels is that most (>90%) of the total body
stores of K are contained in the tissue where it can't be measured by
routine tests and not in the blood - so blood tests don't represent the true
body stores of K.

My best wishes for your Golden Girl.and you.

Phil

http://www.felinecrf.org/treatments.htm#High%20potassium

HTH

Helen