Why is my cat peeing all over the place?

Dear Most Esteemed and Knowledgeable Kitties:
Hi. I have a 5-year-old “torbie” (tabby/tortoiseshell) cat and a 3-year-old ginger female. They have been spayed but in the last few months the older one has been hissing and lashing out at the younger one. My younger one cowers away from her. The older one has started to spray [...]