@Miimi and Velvet Mirth
You need to provide more info about your cat. When was she diagnosed? I assume MiMI is female? How old is she? Does she have any medical issues? What do you feed her? Fancy Feast has food from 0% carbs to 20% There's a food chart you can look up the % of carbs. You want to keep it low 4 or 5%.
The only time you give higher carbs is when she drops too low. You need to choose a dosing method TR (Tight regulation )or SLGS (Start low go slow.) You can read all this at the top of the page on Lantus Forum Yellow sticky Notes
Just because she shows no signs of Hypo does not mean she won't! She's already been Hospitalized for Hypo & Ketones. I'd be very concerned . MiMi went to 37 at +6 today. That is a Dangerous # especially on an animal meter! If you don't test frequently how would you know if her BG went too low?
Are you transitioning her off the dry food? I "personally " think it can affect cats BG. Not everyone agrees with me on that.( I've seen cats here go into remission just by stopping all dry food! ) She does NOT need a half can of food Just one teaspoon is enough.
Have you read the Yellow Sticky notes ? There's a LOT of information that would be very helpful for you. The more you know about how the insulin works the easier it will be to help your kitty.
You need some advice from the experts here. It looks like your Vet is not really familiar with how Lantus insulin works. That's not unusual. I see a lot of Vets here giving incorrect dosing advice.
I've been doing this for over 14 months I do NOT give dosing advice. I don't feel I have enough experience to do that. Insulin is a very powerful Hormone. There are people on this forum that have many years of Experience that can help you.
It is vital that you test before each shot of insulin. The testing I do is to make sure Ravan is SAFE ! That he isn't dropping too low. He has been in the 30's unexpectedly.
When Mimi's in High BG it's OK to get a few hours of sleep. But then test to make sure she's not starting to drop .
It took me over a year to get Ravan's BG into good #'s But even now he will sometimes go too high Or too low. I'm using Calipers to adjust his dose by tiny amounts. I hold the dose for at least 3 days if it keeps him in good #'s I'll keep the dose. If he drops too low I reduce.I'm trying to keep him below 120. It's a balancing act Just a tiny drop too much can drop him too low. He's pretty much regulated now.
In the beginning I was very concerned about poking his ears so much. I picked a comfortable chair to test him in. With a bright light over it so I can see exactly what I'm doing. Most of the people here give their cat a "Treat" when they are poked. The cats learn to associate the "chair" & the treat with something good.
I don't give treats. Just a lot of LOVE & petting. It didn't take very long before Ravan would come to the "chair" when I called & I shake the container of test strips. When he hears the clicking he comes. He may not like getting poked but I do believe he Knows I'm trying to help him. Some people use neosporin on the ears after a poke. I use Coconut oil.Ravan's ears are just fine no scar tissue. Have you watched any videos about testing? Where is the best place to poke?
Sorry if I'm overwhelming you with info! Everyone here wants to help you! We've all been there & know how confusing it can be.Please ask questions. The more you learn about all this the easier it will be.
After writing all this I just discovered you have some excellent help already! Marje and Gracie is truly an Expert. I guarantee if you follow her advice everything will get easier & work out fine. She's helped me enormously! As have others that are also very experienced. They truly know more that the Vets do about Dosing Lantus insulin!
Think of the SS (spreadsheet) like a puzzle. You want to gradually fill in the boxes. The more info you have the faster you'll understand what the insulin is doing at different times of the day. We all learn to study the SS & look at other's also.
The high bg is scary but there's not much you can do The low BG is what's a big problem. Rather high than too low. It takes time for kitties little body to adjust to the insulin.And the best thing you can do is take a few deep breaths & try to be calm when you test. Our emotions affect our animals.
There's a product called Feliway it's supposed to calm a cat. You spray it on a towel 15 mins before testing & let it dry. Put MiMi on the towel, pet her talk quietly & eventually I think she'll understand you love her & want to help her.

Wishing you the best of luck with Mimi. If you follow the advice & read as much as you can it will get easier! Patience is very important
One more thing! Have you considered getting a Human meter? The vet always suggest the animal meters but the test strips are so expensive. Most of the people here use a Human meter. I 've been using a Relion Prime meter from the Walmart. The test strips are about $20 for 100 . Just a thought if you test frequently like me!