You could build a website for your girlfriend; and use it as a reference/portfolio. Why you didn’t do this?
Second, I believe you have done some websites before this adventure; they can be used as portfolio too.
Third, why you’re not “giving away” your first websites for a very cheap price? This way, you can really start to build a portfolio.
Finally, I suspect that the real value of a website for a veterinarian is a booking system, or something like that. What did you discover from the ones interested?