12.5 Year Old - Just Diagnosed - Not Eating/Tired

Hello,

My cat sandy (12.5 Y, Female) just recently got diagnosed with diabetes. Upon starting insulin therapy at 7 am, with 2 units (2x a day) with her regular kibble (Feline Care Nutrition™ Weight Care Dry Cat Food which was recommended to me by a previous vet). Before her first ever dose of the Caninsulin, she ate a really good amount of the kibble (gobbled it all up fast too!). We did her first dose and it went pretty smooth.

After that, the problem started. At 7 pm, she refused to eat. We couldn't give her insulin. Then she refused to eat up until the next morning at 7 am. We got afraid that she might've become hypoglycemic because she was noticeably refusing food and seems a little lethargic/tired. She had even thrown up the same morning (5 hours after her dose) to which we called our vet and he said to maybe feed her 3 times rather than 2. We took her to the emergency vet right away who said her blood sugar was a little high so they gave her a half dose instead and they also put her on anti-nausea and appetite stimulant to get her eating.

On this day at 7 pm, we tried to feed her her old kibble again and she was not interested in eating at all. But she was notably crying for food (sounded hungry!). I really needed to get something in her system so I gave her some Fancy Feast (Classic Paté Cat Food) chicken feast flavour topped with a little bit of freeze dried chicken. I gave her a bit at first to see how she responded and she ate it all up! Then an hour later, I gave her a more proper portion (about the rest of the can up until 1/2 a can), and she ate it up too. We were able to administor insulin (full dose) as per instructions from our vet. After this, she seemed pretty energetic and responsive (was playing with her toy and all), walking here and there.

Up until this morning now at 7 am, we were told to continue to give anti-nausea med (which she ate) but only give the appetite stimulant if she was not eating. I gave her the same meal as before and she ate it but definitely seemed to be more reluctant to finish. Its now about 7 hours past her last shot/meal. She has been definitely a lot less energetic than yesterday and seems to be pretty sleepy. No other symptoms though such as vomiting or weakness. Just seems to be more reluctant to respond to any playing with her toys and me. Or walking downstairs. It just seems like she wants to sleep and is drowsy.

I called my vet again and waiting to hear on what it might be but I feel like I am in such a pickle. On the one-hand, she's not eating her old food at all and if she doesn't eat, I can't give her insulin. On the other hand, she eats new food but i don't know if I change her diet rapidly but its the only way I can give her insulin and get her to eat something. Further, I don't know if its only because of the appetite stimulant and/or anti nausea meds that shes even eating. It seems like even with those she doesn't want her old kibble but I don't want it to be the case where she only eats depending on those meds.

Can somebody please give me some advice on if this is normal, future steps etc. Is she just more tired and lethargic in general because she has a lower blood sugar than what she usually had (only been 3 days since she started insulin, but only 3 full doses and 1 half dose in total within those days). Is she hypoglycemic and if so, what are notable symptoms other than lethargy because that can just come across as being sleepy (Which she used to do pretty often before too, but not to this level)? Is it bad if I switched her diet? Is she always going nauseous at the site of her food? I can't tell if her lower activity level and being more drowsy is because she just started her insulin so her blood sugar is lower than normal or if her blood sugar is dangerously low. I understand that glucometers help but I haven't been introduced to that with my vet and I want to be able to build this intuition for seeing it right now before I obtain a glucometer with my vet.