That is just a money grab. There is nothing special about diabetic food. With the exception of one diabetic pate, they are all too high in carbs.
Let's get the mixtard situation sorted first. I did a Google Scholar search for "mixtard" "30" and "feline." Dr. Google came up with just 15 possible hits of which only 3 were relevant. All 3 originated in Romania. I also did a search using a university library's search engine and came up with the same searches. So basically, there is nothing in scientific journals worldwide that supports the use of mixtard.
I've wracked my brain and can only come up with the Lantus given at night because it is a gentler insulin and your vet might think it safer to give at night than the mixtard. But this would not work because Lantus is a depot insulin. It needs to be given every 12 hours to maintain that depot. Adding mixtard does not help the Lantus depot maintain itself. Lantus craves consistency in dosing and in time. A few people over the years have been told by their vet to dose Lantus once a day probably because the vet was more familiar with canine diabetes. Cats have a different metabolism than dogs. Once a day Lantus has never worked for cats.
Lantus will never get the consistency needed if Mixtard is given in the morning and Lantus is given at night. Dump the mixtard.
As long as you dose 12 hours apart, you can choose your own times. Most people arrange their shot time around their work schedule. It is completely up to you what time you choose.
Like I said above, Lantus craves consistency. As a newcomer, your no shoot number would be 150. As you find out just how Leo responds to Lantus, your no shoot number will gradually lower.
With Lantus, you –
1. Test to make sure the number is high enough to shoot;
2. Feed to make sure the cat is willing to eat;
3. Shoot
You can then feed snacks throughout
both cycles, earlier rather than later. Just pick up any food 2 hours (+10) before the next insulin shot. You do not want the preshot test to be food influenced.
The night cycle – disregard your vet's advice. Even though Lantus is a much more gentle insulin, food at night is important. It helps slow down the numbers drop. You can feed a snack before you go to bed and leave some snackage out.
Print off and show her the following:
Here is a very recent guidelines for feline diabetics and insulin use:
http://www.felinediabetes.com/FDMB/...nagement-guidelines-for-dogs-and-cats.195960/
Click on the blue link for the pdf.
(2018) AAHA Diabetes Management Guidelines for Dogs and Cats
Revised January 4th, 2018
Also show her the protocol studies regarding Lantus use in cats.
Roomp and Rand (two very distinguished vets) developed
the protocol for Lantus.
If your vet does not want to work with you, call around and find a vet that will. Ask whoever answers the phone what insulin the vet clinic uses and how they manage feline diabetic clients.
Also, I agree with
@JanetNJ – let's see what the Lantus people have to say.