@FurBabiesMama i am terrified to switch. I don’t really know why but I don’t truly understand how they work differently and how I’d need to adjust dosing. What made you try Levemir over Lantus or Novolin? I’m reading a lot and dang all of those expensive and how do you get them since they don’t seem to be available on typical pet sites? All I see as another option on those sites is Vetsulin which seems to be the same as PZI if I am interpreting correctly?
Detemir (Levemir) and glargine (Lantus or Basaglar) are very long-lasting insulins. Those are the ones you would want to consider. You would not want to consider Vetsulin or Novolin since those are not even as long-lasting as ProZinc. After doing my research, I just liked the Levemir option best. Here is an old thread you may want to read through where Lantus vs Levemir was discussed:
http://www.felinediabetes.com/FDMB/threads/why-is-lantus-so-much-more-popular-than-levemir.195958/
They are human insulins, so you can get them from human pharmacies. In the US, you have to get a prescription from your vet. You can get either in a five-pack of pens. I LOVE the pens. They are like mini vials. Once you start using a vial of insulin, the time is ticking on it. After a few months, it is no longer effective. So, I was always ending up throwing away insulin when I used vials. Since each pen holds less insulin, I am able to actually use up all of the insulin without ever throwing any out. As long as a pen is unopened, it is good until the expiration on the box which is usually a couple of years out. I got my Levemir from Costco. It was pretty expensive, but since I get to use every bit of the insulin in every pen with no waste, in the long run, it is not really that bad. A lot of people here get their insulin from Marks Marine in Canada (I think they may sell Lantus but not Levemir) because it is much cheaper, but I have not done that.
We all know 'every cat is different', so you cannot really know how your cat will react to an insulin until you try it. I can only share with you my experience. With Levemir, the curves are much flatter. Mia was up and down so much more on ProZinc, but now, she stays nice and steady within a great range. I love no longer having the stress of deciding what to do if a pre-shot test is on the lower end. I can give her shot pretty much regardless of what her pre-shot test is and feel comfortable that she is not going to go too low. This is because the onset is later than with ProZinc and the drops are not as 'harsh'.
I was concerned in the beginning because I had focused so much on learning ProZinc and felt like I was 'starting over' by having to learn something new, but really, it did not take long to get used to the differences, and for me, they were all good differences (like what I mentioned in the last paragraph). As far as how they work, you have probably read this:
http://www.felinediabetes.com/FDMB/threads/what-is-the-insulin-depot.150/ I think of it like this... With an 'in-and-out' insulin like ProZinc, a shot mostly wears off by the next shot time (there is actually some overlap, but for the most part, it wears off which is why the pre-shot numbers can get pretty high even when the mid-cycle numbers have been good). With a 'depot' insulin like Levemir, it 'builds up' and is slowly released. As you consistently give shots, it's like you are keeping that reserve stocked so it can continue to release and be effective.
. Are there any other health factors that might be effecting her?(Behaviour, potty habits, teeth looking ok?) Any food allergies? 
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. How much does she weigh again? 
I usually put 350 for max phosphorous in the food chart filter.
. And I agree that the switch between chicken and turkey shouldn't be a big deal as long as Little likes them both.