You don't quite have the data yet to shoot below 150, and haven't been consistently testing prior to insulin. To be sure it is SAFE, you should always test her before giving insulin.
As you get more data, you will be more comfortable with shooting at slightly lower numbers than 150 because you will know how she frequently responds. Lantus dosing is based on the LOWEST number in the 12 hours, usually between 5-7 hours after the insulin.
If you can get 12 hours to do so, and when you've been using the same dose consistently for over 3 days, run a curve. That is, do the morning test, give insulin, then test every 2 hours until the next dose is due. This will show you how the insulin works for her over the 12 hours between shots and will guide you on dosing, following the protocol instructions..
Also, since you are using Lantus, pop over to the Lantus forums and read the sticky notes about how best to use Lantus and the safe way to make doseage adjustments.
Additional monitoring tools include:
* Measure how much water you put down at shot time vs how much is left at the next shot time. As you get control, you should see this reduce. (Be consistent in how much water you add to the canned food too, as that will affect water drinking, as will heat, etc.)
* Note how hungry she is at meal time - a) Ravenous and eats it all at once? b) Eats some, then nibbles throughout the day? c) Nibbles throughout and finishes? d) some left at next feeding? e) not eating at all
(no eating = no shot until proven necessary by testing !!!)
* Any vomiting? Use caution with insulin dosing! You must have food to match the insulin.
* Any diarrhea? Constipation? These may affect food intake, and thus the glucose level and response to insulin
* how big are the urine pools in the litterbox within 12-24 hours (you must scoop daily to check this)? 1/2 cup? 1 cup? more? Unregulated diabetics pee lakes. So do cats with renal disease, so if the glucose levels are good, evaluation of kidney function may be helpful.
* dehydration - if you can gently pull up the scruff of the neck, let to, and it snaps right back down, not as likely to be dehydrated. If it stays pulled up, dehydration may be moderate to severe. If you press a finger on the gum then remove it and it stays whitish ("blanched"), she is mildly - severly dehydrated. Dehydration should be checked with the vet.
The one certainty we have all experienced - Each Cat Is Different (ECID) and things change. You cannot assume everything is going to be consistent. If the cat has any other medical conditions, these can play a part in controlling the diabetes.
