I managed a cat with heart and kidney disease, Neko. They are a hard combination to manage. When the disease progresses far enough along, fluids are recommended. But heart conditions cannot take extra fluids. Which I found out the hard way. I was lucky that Neko managed to get over that heart failure incident that resulted. Fluids will not cause a gallop, but can make existing heart conditions worse. A gallop may or may not be a sign of a heart condition, and should be checked out by a knowledgeable vet.
However, depending how far along the kidney disease is, you might not need fluids for years. I've seen people with kitties with literally years with early stage kidney disease, and doing nothing more than giving lower phosphorus foods. Which is what I did for a couple years before the heart condition showed up. I also had to give a med for proteinuria (high protein in the urine), but that was it.
I wouldn't worry too much about a one time high blood pressure. She spend time in the ER, probably noisy and stressful and she got poked and prodded. Neko's BP soared the first time I got it tested. Vet clinic had a busy waiting room, vet was late getting to her due to an emergency, an uncontrolled dog bumped and sniffed her kennel, a newbie tech tried using BP equipment for the first time. Heck, I was stressed! BP was over 220 and when I eventually I saw the vet she called it an epic fail and didn't charge me. Second attempt at a much quiet vet clinic, but unfortunately a puppy came in at the wrong time and sniffed her kennel. Over 180, better but still high. Next attempt at the dental vet - in a room by herself for a while with Feliway's going - BP 140.
Always try to get a BP test at a quieter situation. When I started taking Neko to an IM vet, we were put in a quiet exam room for 15-20 minutes alone for a while, before they did the test. It was usually in the 140's range. A second test of the BP is a good idea. You don't want to start BP meds unless she needs it.
Did the ER give you nausea meds such as ondansetron? If she's not eating properly, then she might need some meds short term to help her do that.
However anyone knows little food plus little insulin equals dka, so I cant believe that advice.
You need infection and/or system inflammation to be part of the picture too. But she has that infection. Keep testing daily for ketones at home. I would stick with 4.0 units for now. She's not on too high a dose.
