It´s not your fault, no not at all. I´m sure you did the proper nourishment and care for it, but i´m sure she just had a condition but you couldn´t tell in time for it to get better/diagnosed. I know you deepley cared for her, and that´s the thing, whenever people are like this after a death, it shows that they actually cared and wanted the best for the thing they cared about.