Who's to say what makes for a sudden spike? Maybe Casey saw a squirrel through the window; maybe she was just having a bad-mood kind of day ...
overall she's had some pretty good numbers there ... am I correct in assuming that she's pretty sensitive to micro-doses of insulin? (We have that problem at our house!

) I guess if Casey were my cat, I'd continue testing AM & PM for now, with a spot check here & there in the cycle sometimes, just like you've been doing. This may have simply been a blip, after all.
For your reference, these are the BG # ranges for "normal" that I'd copied from two difference source docs on FDMB (note there's a 10 pt. differential between the 2 sets; don't really know why that is...):
Off insulin: 40-120 mg/dL (56-168 mg/dL on AlphaTrak)
On insulin: 50-130 mg/dL (70-182 mg/dL on AlphaTrak)
50 - 130 mg/dL (2.8 - 7.2 mmol/L) {71-83 to 186-217 mg/dL for an AlphaTrak}
- On insulin - great control when following a tight regulation protocol.
- Off insulin - normal numbers. (May even go as low as the upper 30s (1.7 mmol/L){60s for an AlphaTrak}; if not on insulin, this can be safe.
P.S. Are you measuring her water consumption every 24 hrs, too? This is a good thing to keep recording, even after you're totally certain she's OTJ.