Looks to me like Angel is in remission. As long as she stays <120, I think she'll be ok.
Not sure there is anything else you CAN do to get Angel into lower numbers. Certainly not even a drop of insulin will make a difference, that would not also drop her BG levels too low.
Angel's body is producing enough insulin to keep her in those lower number. If it wasn't, you'd be seeing numbers back in the high blue (> 150) range and higher. I think you have to accept that she is always going to be a bit higher in the evenings, BG wise.
Diet controlled remission lasts as long as it lasts. There is no predicting if she will come out of remission some day or stay in remission for the rest of her life.
Keep your eye out for bouts of pancreatitis, and/or an infection/inflammation of any kind, as those are the 2 most common reasons for a diabetic cat needing insulin again. Steroids can also cause a loss of remission, but sometimes they are needed to control another health condition. Don't change the food carb percentage, unless you are sure it's the same as Angel currently eats. Watch out for any added sugars in any medications the vet may give you for Angel. Remind your vet that Angel is a diabetic, simply diet controlled. "Once a diabetic, always a diabetic."
Other than that, Congratulations!
You'll have to wean yourself off testing every day. Slowly but surely, you'll get more comfortable with fewer and fewer tests. Once a week or so for now and then once a month should be enough. Or if Angel every seems "off" behavior wise or some of the diabetes symptoms come back, you'll want to test again for a few days, to assure yourself that everything is ok with her.
No need to mention my name. I like to be a bit more reserved and private, if that is ok with you.