Thanks for the additional information.
So that red staining isn't from blood...it's actually called saliva staining and happens when a dog is regularly licking at somewhere, like your dog was. We often see it around the vulva, on the feet and under the eyes from tear staining.
I'm sure that you feel horrible, but I truly don't think that getting a urinalysis would have shown blood in the urine.
Had she had a urinary tract infection, you would have seen more signs such as frequent squatting with only small amount of urine or none at all, foul smelling urine, red urine, painful abdomen...and then as the infection progressed you would have seen vomiting, anorexia, extreme lethargy and a possible cessation of urination completely.
I'm so sorry that you're still hurting over her loss, and I wish I could tell you that it gets better, but there will always be a hole in your heart where she was. It might not be a bad idea to seek out a grief support group in your area. If you contact a local ASPCA or shelter, they may be able to point you in the direction of a good one.
I'm absolutely positive you didn't miss anything here, and I am just as certain that the urinalysis wouldn't have changed anything.