My daughter's cat was limping, took her to the vet, did x-rays, no broken bones, pelvis had shifted. Diagnosis, either, kicked, fell badly, or bumped hard, but not hard enough to cause bleeding or broken bones. Gave her a cortisone injection (Sunday) told to bring her back each day, another cortisone injection Monday, more x-rays Tuesday, still no definite conclusion to cause. Now unable to walk, but still eating and responding to affection. Another cortisone injection. Wednesday another cortisone injection, Thursday another cortisone injection,cat vomited while at vet, taken home, vomited during the night, Friday morning, stopped breathing and died. Was the cortisone a contributing factor to her death?

I'm so sorry that she died. It's always hard to lose a pet. Did you take her for an autopsy? That's the only way to know, for sure, why she died.

Short-term side effects are uncommon but include shrinkage (atrophy) and lightening of the color (depigmentation) of the skin at the injection site, introduction of bacterial infection into the body, local bleeding from broken blood vessels in the skin or muscle, soreness at the injection site, and aggravation of inflammation in the area injected because of reactions to the corticosteroid medication (postinjection flare). Tendons can be weakened by corticosteroid injections in or near tendons. Tendon ruptures as a result have been reported.

Taken from: Cortisone Injection of Soft Tissues & Joints Side Effects, Dangers and Treatment on MedicineNet.com

From the sounds of it it is possible that it may have contributed but you can't know for sure.
There may have been broken blood vessels from whatever happened to her and the cortisone made them bleed more.

I'm very sorry this happened to your daughters cat, it's always hard losing a friend but even harder when you have fought so hard for them.