Hernia on 18 year old dog

Hello, I'm Ignacio, i live at a farm in Chile. About 13 years ago a dog showed up, we kept her, about a week ago she started acting weird, she wouldnt eat and she walked slower, but worst of all her abdomen hurt. We took her to the vet, found it had inflammation, like liquid. Took an ultrasound, it was decided it was a hernia but all her intestines were where they shouldn't be. We did blood work which showed all her levels were ok, meaning her kidneys and liver worked as they should. The main vet said we should operate, the vet that took her ultrasound said the same thing, the vet that took her blood also. I asked a vet in the capital for his opinion and he said she looks good and the operation usually goes well. She is an 18ish year old dog, her hernia is big, should we operate?

Hello - it sounds as though your dog has recently developed this hernia at the impressive age of 18.  I'm afraid that my main question would be - why?  What has changed that a hernia has suddenly occurred (and what part of the body, exactly, has herniated?  I assumed intestinal but this is not the only possibility).  I would be concerned about fluid build-ups (why has fluid build up?  Is there some underlying disease?) or cancer (is there a large lump on the spleen about to rupture, for example?)  Your vet may try to find this out prior to any kind of surgery, in order that they have full context and your dog is only put through trauma if it is appropriate.