i've got a couple of thoughts.
You've got the right idea going - you've done a good job of getting tests in to see what's going on. You do want a dose you can give twice a day, same amount.
One of the things that happens when a cat is working off of insulin, which it looks like Sammy's trying to, is that when you have a good dose the cycle will flatten out. Instead of being much of a curve, it's almost a flat line. At the beginning of treating a cat, we encourage people not to shoot less than 150, so that they can learn how their cat is responding to the insulin. But as soon as they've got the hang of testing and know their cat's responses better, we gradually lower the shooting number.
As the preshot number gets lower, typically the middle of the cycle flattens out to nearly a straight line.
So shooting a 110 this morning with the 0.5u would've been ok, as long as you were going to be home to monitor, had enough strips (say 20 strips available) and something high carb in case you needed to pull up her BGs. If you weren't going to be home, then skipping or shooting 0.25u or even just a drop would be good options.
anytime you shoot a number lower than you've had before, you want to get a +1 and +2 test, just to make sure there's no diving of numbers going on. when the +2 is lower than the preshot, that's a red flag to be extra vigilant, and perhaps even give food then to slow down the cat's drop.
This is a lot of information, so to not overwhelm you i'll stop there. it's obvious you've been doing lots of reading and figuring things out - good job. If you can post every day, ask lots of questions, we'll help you keep her safe. I actually think you could continue the 0.5u dose tonight rather than reducing right away. She hasn't had anything below 50 on this dose - 50 is our dividing line for reducing the dose for a newly diagnosed kitty. By skipping the dose this morning she will be higher tonight, and probably need the full amount.
What do you think about all of this? any questions?
eta - cats often go lower at night than during the day, so it's a really smart idea to get a before bed test every evening. Also, the person who posted above me, Will, just had his cat go off of insulin. Take a peek at Clyde's spreadsheet
https://docs.google.com/spreadsheet/pub?key=0AnLPtmGIw3yedEdnckhTeElGVFcxckFTNmxoV0ZKUHc&output=html to see an example of the flat cycle you get when you shoot a lower number. You still have to monitor, but it's kinda amazing to see.