Well, Lulu finished her 2nd 2-week round of antibiotic on Tuesday, and so far... NO blood! (nothing visible, anyway)
We have a vet appt on Monday ~ a follow-up visit for both this issue as well as heartworm treatment (it'll be 6 weeks post HW-trmt on Monday) ~ but so far, I'm feeling hopeful that this was just a resistant long-term UTI.
Thanks for your input and positive thoughts!