Female rabbit has blood in urine?

Hi! So I have 2 rabbits and one of them had blood in her urine. She is quite old... About 7 years. Anyways we took her out to clean her cage and when we put her back in we noticed her urine had blood in it. We kept her in the bathroom while cleaning because we also have a cat. She will pee when she is scared. It was very yellow/cloudy urine with streaks of red in it. No chance she was injured because she has been in a separate cage for 2+ weeks. We bring them inside when it gets too hot out for them and have to put them in separate cages. What could be causing this? Don't really know what to do because she is so old but we don't want her suffering! Help please!