No, 122 isn't low, objectively speaking. I think you mentioned that Heart goes in for big drops, and you weren't going to be home, so it's natural to be concerned. The more you test, the more comfortable you'll be. But by itself, that's a beautiful number.
Has anyone discussed the differences between human meters and the meter the vet uses? Their animal-calibrated meters read higher, maybe 30 points (Sienne knows this one). Even so, 122-30 is 92, which is still a good number.
You might like to read the spreadsheets in other condos. It will help give you an idea of numbers that diabetic kitties run. (Of course, ECID: every cat is different.)
Many vets don't know much about feline diabetes. They don't get a lot of training on it in school. In time, you will find that you've learned so much specialized information, you'll be giving your vet information he/she doesn't know. What you hope is that the vet is open-minded enough to listen to your experience.
Curious to know what you're feeding Heart.
You are in the right place and doing great!