True enough, she should have had it treated immediately, but the costs probably caused her to pause. I don't fault the humane society either. They have to do the best they can with limited resources, and sometimes they can't afford to spend all their resources on the sick and wounded, when healthy animals are put down because of overpopulation.
No more backyard litters of puppies and kittens is the answer. Leave breeding to the few... It is not cute to have litters for the fun of it when we are killing so many every day.
Feral cats around my home are getting the 'fix and release' treatment. No new kittens, and no voids for other ferals to move into.
It might depend on where she lives. Many places, like where I live, you'd be hard pressed to find a vet after hours. I found that out when my dog found a rattlesnake late one night. All I could do was try to make him comfortable, stay up (all night) and keep an eye on him.
Just imagine a medium-sized dog with a St. Bernard's head....