I did not know dogs could get parasites in their bladder so I did a little research and came up with this:
The Dog Bladder Worm (Capillaria plica)
So I guess it is possible for the eggs from different worms to get in the urine.
As for the diarrhea, here is the information I found on the side effects of the Simplicef:
An oral antibiotic most commonly used for skin infections. The most common side effects include vomiting, diarrhea, and anorexia. This antibiotic is similar to Cephalexin but is given once daily.
This is what I found on the Panacur:
An oral broad spectrum dewormer. Fenbendazole is the active ingredient. Panacur will kill roundworms, hookworms, whipworms, and most species of tapeworms. Side effects are very rare at normal doses and may include vomiting.
I sounds like your vet is on the right track with the Panacur because if I read the article correctly, maybe whipworms eggs or others could get in her urine.
I am not sure about why he is giving Simplicef. Did the vet say she had a skin infection also? Most likely it is the Simplicef that is causing the diarrhea. You could possibly give her some pure canned pumpkin to firm up the stools, 1 tsp. twice a day. You can add a little karo syrup to the pumpkin to make it taste better. I would watch her closely and if the diarrhea continues you might want to call the vet and ask him about it. The Simplicef might be too strong for her. I hope you baby gets to feeling better soon.