I a 66 year old man, non-smoker, reasonably fit for my age. 

Just before Easter 2019 (about 15 months ago) I passed some blood in my urine. It only happened once.   I immediately saw my GP who referred me to the urological service at the nearest big hospital.  I was seen within 10 days.  The consultant indicated that the standard protocol for all referrals is a CT scan, a flexible cystoscopy, and for men, a prostate check.  She also said that in 80% of cases, a cause in never found.  In my case, the prostate check wasn't necessary since I had it removed way back in 2010, so I just had the CT scan and cystoscopy.

The CT found a very small kidney artery embolism that they're monitoring but which will probably never cause me any problems.  However, the cystoscopy found a very tiny cancer growing inside the bladder.  It looked fronded, like a tiny plant you'd see in a fish tank and quite pretty.  It was removed a few weeks later (June 2019) in a simple operation called a TURBT lasting about an hour.  I went home the same day, and recovered completely after a couple more days. The follow up cystoscopy a few months later was clear, and I'm awaiting another follow up now (Covid-19 permitting). 

I was somewhat unlucky that I had a tumour, but because I acted quickly, it was removed well before it could become serious, but I am aware that some people do need a second operation if bits of the original tumour get left behind.  Fingers crossed that the surgeon did a great job. 

Bladder cancer is a blessed nuisance, but the earlier it's caught, the easier it is to treat.  I only had one incident of blood in the urine, but because I didn't ignore it, the cancer was caught in good time. 

So, I would encourage your Nan to have further tests. Bladder cancer is very treatable. 

Thank you very much for your reply & brilliant on your news hopefully that's all sorted fingers crossed