Can you sue a animal hospital or like a vet. for not providing immediate care?

so my girlfrend is a big animal lover and a few years back when her dog got sick she took him to a vet and they refused to care for the dog or even keep the dog stabilized until she payed up front $2,000. Now could that be tried as animal cruelty? now shes just curious shes not going to sue, no way in hell im going to let her sue a place that helps animals. but still its a lingering question