ok, questions
and i'm sure i might initially miss a couple but i or someone will think of them
have you just recently changed to those foods you mentioned? or has she been getting those all along?
what was going on that led you to take kitty to the vet and finding out she had diabetes? what symptoms did she have?
has she been or was she recently diagnosed with any other health problems? infection? bad teeth? injury?
do you know if a fructosamine test was done to diagnose the diabetes or did high glucose show on routine bloodwork?
did the vet show you how to draw up 2 units in the syringe or did you have to figure it out yourself? and either way, can you describe to which line on the syringe you are drawing the dose to? i.e. first line, second line, is it noted with a 1 or 2 or any number?
now, to see if i can explain a couple things quickly. lantus works in such a way that you rarely see any effects of the first shot or two. it "builds up" in their system, actually starting to work after a couple or few days of shots. soooooooo, for you to see this much of a response on the first day is pretty odd and could be an indication that she doesn't really need insulin or not so much of it. i know that is totally counter to what you have been told in the last few days by the vet but it is totally possible and having the answers to the above questions will help the very experienced people here figure out which one it might be. more than likely yes, she needs insulin, but just not so much.
gotta step away from the computer for a few so if you can start with the above questions i'll be back in just a few, as i'm sure others will be too