Veterinay science takes a lot of studying and concentration, if she doesn't speak Polish she will not understand anything. I took my internship with a vet locally, but if she doesn't know the vocabulary in english, and there is a lot, it will become confusing to her in Polish. She needs to know Polish to understand. And if she wants to become a vet in the US, why make it harder by studying Polish medical vocabulary which she won't need? Although it is interesting to see the differences in practices between the vets in Poland and America, once she becomes a vet tech or practicing veterinarian, she could travel to Poland and give some insights.
But if she doesn't know too much Polish, it will be difficult.