Hi fenderrae,
Some cats can get a little lethargic when they first start treatment as their little bodies adjust to the arrival of the new insulin but typically that response should wear off after a few days. (Great that you're home testing and a very smart move on your part to do a spot-check to make sure her BG was OK.)
I'd suggest continuing to keep a close eye on her and talk to your vet about any concerns.
By way of general information, while Saoirse was on Lantus she would typically be a little sleepy for an hour or so after her insulin injections but then she'd perk up again as soon as the dose kicked in (onset).
As Melissa (FrostD) comments above, sometimes a particular insulin does not agree with a particular cat in which case switching to another insulin might be indicated. (Saoirse didn't do well on Caninsulin - lethargic for 9-10 hours out of every cycle - but she did great after the switch to Lantus.)
It can be helpful to record general observations in the Remarks column of your spreadsheet: makes it easier to spot any emerging patterns, and it's a great resource to refer to when consulting with your vet.
Mogs
.