I agree with Sue. This could be a bladder infection. Or, if she DOES still have her uterus, she could have a mild uterine infection of some sort.
I'm surprised the vet didn't want to check the urine sample. Usually strong smelling urine is an indication of a bladder infection.
She could definately still get pregnant.
......But of course, she could still be pregnant, as well.....
My female dog has 'you-know-what's' (!) with her 'boyfriend'. He's been neutered so she can't get pregnant. I let them get on with it. But once, after their session, she peed on the floor. She was not happy about that, as she is naturally fastidious, and would NEVER EVER go in the house. I knew something was wrong, so took her, along with a pee sample to the vet. It turned out she had cystitis. A short course of Amoxycillin cleared it up fine, and there's been no recurrence.
Don't know if this could be the same thing with your dog. But she got this after having sex.