Gail if Evita was testing 65-100 at the vet then she was probably running much lower than that if she were being tested in her home environment without stress. It is nearly impossible to get reliable test numbers at the vet.
Also Lantus only lasts 12 hours (appx) in a cat..so needs to be shot 2x daily or the cat is going half the day with no insulin. So you end up with wonky too high or too low numbers. If you want to lower the dose to 1/2 U, then it would be better to shoot .25U twice a day. Same amount of insulin...just given at 12 hour increments since the cat metabolizes it so quickly. She would not feel good high part of the time and low the other.
Here is what .25 looks like:
I would be reluctant to shoot .50 anyway... and especially unless you are testing/monitoring closely. I suspect she went much lower than the 58 we caught the other night, since that was at +12. She is not eating well enough that you can count on her to feed herself out of low numbers with reliably. And so not only is it better so her levels can be more consistent, but also safer to split that dose and do .25 BID.
It may help to order some of the Fortiflora and use that as a food enticer to get her eating. I sent you the other list pf enticers as well (ask again if you can't find it) We know she loves the chicken treats. Those were a hit! Use that chicken dust sprinkled on her food to get her to eat a little more. Sometimes when you are transitioning you just have to try lots and lots of different foods until you figure out what they'll eat. Maybe leave out more than one variety at a time to give her options.
I think you may find she doesn't need insulin for long at all. I would be careful to test and ween her off slowly depending on what the numbers tell you.
She may in fact have just needed a food change and a little jump start, and you got lucky!! Fingers and paws crossed.