Fiorella grew up in an era which touted the power of positive thinking. She thought anything was possible if she totally believed in it, and being Lutheran--saved by faith alone--reinforced this viewpoint.
Of course she was a little discouraged when she leaped off of the porch step with a Mary Marvel cape tied around her neck and didn't fly, but she figured the fault was hers--she hadn't believed hard enough.
Other things didn't work out in her life either. In fact, she noticed that whatever she wanted to happen or thought would happen didn't happen so she revised her strategy, stating the negative to invoke the positive. Thus now she cheerily says things like "when I go senile . . ." as a charm against doing so.
It's a sort of magic to control her own private universe, but deep inside she remembers falling off the porch step and knows she has no control. What happens to her is both random and inevitable.