I am glad that she is acting normally. Blood tinged urine is not a normal occurrence at any time. It could just be a coincidental urinary tract infection, or it could be residual bleeding from the hysterectomy (that is what a spay is). The vagina and the urethra are extremely close together anatomically, so that blood from the hysterectomy will pass down the vagina and can appear in the urine. Regardless of the cause, please call your vet ASAP about this.