Aw, jeez. Sorry to hear about this.
You can do some tests whicch are cheaper. You don't have to do them all. Doing a blood panel can often tell if cancer is likely. I think you said that she already had a blood panel just a week or two ago? If that is so, then maybe you can take those results to the vet you saw today and he can look at that for a minimal fee.
It seems weird to me that all this popped up right after she was stepped on. Just a coincidence? I was really thinking that she would be having an internal injury.