I'm glad that her appetite has picked up again. The frequency of those injections depends on the cat's condition.
A cat with cancer or IBD can have them fairly often.
If Zazou is getting the shots only to boost her appetite, you might want to ask the vet about an actual appetite stimulant like Mirtazapine. Steroids can a have a lot of side effects.
If she is still sneezing due to an upper respiratory infection, she shouldn't any cortisone injections, as they depress the immune system, and they can actually cause kitty colds.