Haha awww, sniffing the sidewalk and chasing your moms Dhihuahua, how cute!!
If she doesn't pee by tonight, I would most DEFINITELY take her in to see the vet tomorrow. These little ones bladders are very small...and there is just no way she could be "holding" it that long. If she doesn't go potty by tonight, I think something is going on for sure.
Good luck to her and please keep us posted!