Hematuria is the presence of red blood cells in the urine causing bloody urine. The causes can be from the following:
Bacterial infections of the urinary and genital tracts (most common reason)
Cancer of the urinary or genital tracts
Calculi (stones) in the urinary tract
Rare parasites of the urinary tract
You will need to have a vet run tests to see the underlying cause. These will be Urinalysis, Complete blood count, possible abdominal X-rays.
Treatment will of course depend on the outcome of the tests. Blood in urine is most times an infection of the urinary tract which is easily treated with antibiotics. Also diet changes can help prevent them from coming back. You can also provide give her a drop or two of unsweetened cranberry juice to help lower the PH in her urine, This will not cure anything, but will help. If she is peeing slowly, this is something you want to deal with as soon as you can. She sounds as though she is becoming blocked. This is a huge deal and emergency of it happens. It can cause her bladder to rupture if she stops peeing. Fixing it now before that happens will save you a lot of money at the vet, and her a lot of stress.
Please let me know if you need any further assistance with this.