Hi there. I'm Dr. B. I have 18 years of veterinary experience and have been practicing exclusively dog and cat veterinary medicine for the past 11 years.
I'm sorry to hear about your 14 year old girl! I know it's distressing to see, especially when you see blood. These are classic symptoms of urinary bladder disease -- at her age, very likely a urinary tract infection (just like what we get). Typically, a cat with a UTI (urinary tract infection) will seem fine one minute, and then suddenly you see blood in the urine and LOTS of frequent straining to urinate, often in unusual places. For her, it feels just like it does for us: urgency, burning. It's very uncomfortable, but not an emergency to deal with overnight. You absolutely DO need to get her in to see her veterinarian tomorrow, though. Your vet will examine her and get a sample of urine for urinalysis. He/she should be able to give you a diagnosis of whether or not this is infection right then during the visit, then prescribe/treat with antibiotics. If this is a simple UTI caused by bacteria, she will be 100% better within 24-48 hours after receiving/starting antibiotcs, typically.
Your vet may also discuss taking x-rays of her bladder to look for stones, or even ultrasound. If this is her very first time to have this problem, and there is obvious signs of infection on her urinalysis, it is totally your call on whether you would want to do more testing (but don't feel like you have to). Another possible test that may be suggested is a blood glucose (blood sugar) test. I absolutely DO recommend going ahead with that test to make sure sugar in the urine (from diabetes) is not what caused her UTI (the bacteria feed off the sugar).
FYI, since she is a female, it is very less likely she is truly "blocked". Male cats, due to their anatomy, can easily block with stones or debris in their penis and are truly unable to urinate. This is a true emergency. However, I have yet to ever see a female block. The straining you see is from the discomfort and urgency in her bladder, not from a blockage.
Here is an link to information that summarizes this condition: http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2457
And here is another that specifically discusses feline urinary disease (of which urinary tract infection is one, especially at her age): http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=611
Until you take her to her veterinarian, there isn't anything you can do for her at home, unfortunately. The biggest advice I have for you is to try and confine her, perhaps to her carrier, a couple of hours before going to the veterinary visit. DO NOT put a litter box, towel, or paper in the carrier (just fresh water). The goal is to give her a chance to collect some urine in her bladder that the vet can perform a urinalysis on. Even if she urinates in the carrier, they can use that if it isn't soaked up into something. Alternatively, many cat owners must leave their cat with the vet for the day to wait for urine to form/collect in order to do the urinalysis.
I hope this answers your questions and you are less concerned. Please let me know if I can help you further. Otherwise, click to accept my answer so I know you got the information you needed. Good luck!