Years ago when my Pushy was young, he went through a period of recurrent crystals & UTIs. One time we were outside in the snow and he ran around crying and finally peed. It was red like a stream of blood! Freaked us out and obviously we rushed off to the vet.The reason I said 'pure blood' before it was because her piss, was pretty much like red wine, not thick but uniformly red, which was pretty much a first for me.
Closest I seen was the piss of a stone blocked male after he was blocked for over 24 hours (over a decade ago), but that was the result of a catheter and it was more like really dark orange than wine red.
Pushy hasn't had problems in years. We are very careful to make sure he gets lots of fluid and he eats a mostly wet diet, with some water always mixed in. I'd say that's worth doing for your Margaret.