Did your vet mention anything about home testing? (Most don't). We strongly recommend home testing here. It's the only way to know what's going on inside your cat's body. Just like humans are told to test before every shot, we believe it should be the same for our furkids.
If you live in the US, you can get a Relion Premier blood glucose meter from Walmart for $9 and 100 strips for the Premier are $17.88. You'll also need a box of lancets (to poke the edge of the ear to get blood to test) and a box of Relion THIN (not ultra-thin or micro-thin) lancets is $1.62. Those are the most important things you'll need. A lot of us like the cotton cosmetic rounds to put behind the ear when we poke (so we don't poke ourselves) but also you can just fold it over to apply some pressure after testing to help reduce any bruising.
If Pebbles was recently treated for ketones, even if she didn't go all the way to DKA, she MUST get her insulin, even if it means feeding her something high in carbs. You can also give a lower dose if she's running a little low or not eating well, but she should get at least a token dose....and if you're home testing, you will be able to make sure she stays safe.
Lantus is an excellent insulin for cats but most vets don't really know how to use it.
What dose are you giving?
For some reason my picture isn't showing up but I also can't remove it. I'll see if I can find another one that shows you where we poke to get blood for testing