Since you are using a ReliOn meter, a 66 is a perfectly safe (and good) BG number (although below the SLGS target nadir and has earned a reduction.) No high carb food should have been given.
I am sorry I didn’t see this until just now now so you didn’t have any help when you were unsure what to do! It’s all okay so don’t worry about it. We don’t use high carb food unless kitty drops below 50 with a human meter. All you needed to do was to feed a little low carb wet food and retest in 30 minutes if you were nervous. Also, she was already at +5 in the cycle so it wasn’t really early in the cycle when there would have been more reason for concern. These lower numbers are new so I completely understand!
Just so you know for the future: When you really are managing low numbers then dry food is not the best choice. Dry takes longer to raise BG and it will mean you have to keep monitoring for a longer period of time. It was okay today because there really wasn’t any low number to worry about, but if you have a number under 50 then you should give one teaspoon of HC food and retest in 20 minutes. Then you keep repeating this until the numbers are rising. As the numbers rise you can extend the time between tests. You have to feed small amounts because that is all you need to raise BG and you need to keep the kitty hungry because you may need to keep feeding small amounts of HC for several hours if the numbers are really low. If you feed too much Bella will get full and you won’t be able to give the snacks to manage the BG (you will have to put karo on her gums.)