There is an Emergency Animal Hospital in my area like that, also.  Unfortunately, they have us over a barrel.  I had to take one of my dogs a few Sat. nights ago, for dehydration due to vomiting and diarrhea....they charged me $516 for 12 hours of IV fluids and one round of antibiotics!!  He is now fine, it was a gastro upset due to some grass he got into outside.     
They would not treat him until I signed their "estimate", and gave a 50% deposit.  Best wishes to your mom's dog!!!     
				__________________  Piper    Leo   Baby Piccolo        |