Hi Jeani, this is unfortunately a common problem. The good news is that your vet is right and there's nothing physically wrong with her; the better news is that she will most likely outgrow it; and the best news is that you certainly can do something about it.
Your vet is also correct that behavior modification will be necessary--but mostly on the college kids, not so much for the dog! You say she is "prone" to urinary tract infections. This is not normal in such a young dog. This suggests to me that she is being asked to "hold it" for too long. When urine sits in the bladder for long periods, bladder infections are the result. More frequent opportunities to void are needed. I would also suggest "Tinkle Tonic" as a remedy to help prevent further infections, because the more this happens, the worse things will get. The bladder lining will become thickened from the constant irritation, and she will be less able to control it.
Some behavior mod for the dog *is* appropriate. Everyone needs to be willing to participate. When people come in, they should ignore her until she sits quietly, and then she can get pets and treats. When people come in and she gets excited, and the people feed into that by making a fuss over her, the problem gets worse. ONLY reward good behavior--sitting quietly, waiting patiently. There are many resources online as well as books. Although I am not a great fan of many of his methods, Cesar Millan does a good job with this sort of behavior. Victoria Stillwell's cable show "It's Me or the Dog" is also worth watching for tips about appropriate actions and reactions for the people involved.
I'd also recommend flower essences to help her stay calm and in control of herself. There are a lot of formulas available, and which one she needs depends on many variables, so just read through the descriptions till you find the best one for the totality of her personality and behavior. If the incidents are mainly predictable and you can give a remedy before it occurs, then an essence like Stress Stopper, Just Relax, Calming Solution, or Rescue Remedy would be appropriate. If she's generally nervous, high strung, or excitable, you might lean more toward Hyper Helper, Nervous Nelly, or Emotional Stability; or if she's shy, Self-Esteem or Safe Space may be best.