Because the uterus and the urinary bladder are located right next to each other, it is possible to have a little bit of blood in the urine following a spay, but it should not cause the symptoms you describe.
Gina is correct when she states that the symptoms are typical of a urinary bladder infection. In order to confirm that this is what is going on, your vet will likely want to check a urine sample. If you can catch a fresh urine sample to bring with you, that would be great. If not, try keeping her inside for 4 - 6 hours prior to the visit to the vet to increase the chances of them being able to collect a sample during the appointment. The treatment is antibiotics and dogs will usually be kept on antibiotics for about 3 weeks. You should see improvement in the symptoms within 48 - 72 hours of starting the medication, but be sure to use all of the medication dispensed in order to try to prevent a recurrence.
If you do not see improvement after being on the medication for 72 hours, be sure to let your vet know. Some dogs will develop stones within their urinary bladder and that can cause persistence of the symptoms even while on antibiotics.
Although this is not a life or death emergency, with any infection, the sooner the pet is treated the less chance there are of complications. I know this is a holiday weekend, but I would try to have her seen as soon as possible, at the emergency clinic if necessary, so you can get her started on treatment and get her feeling better. The longer she goes untreated with a bladder infection, the greater is the chance she will develop the urinary bladder stones I mentioned.
Please ask if you have additional questions.