Sorry this is so long

My parents have an elderly Leonberger (she is 10) that has been having a few problems of late as would be expected however for the past year or so she has had a re occurring problem with a hole appearing under her tail by her bum! I looked in to this knowing that this is a symptom often found in GSD's called Anal furunculosis and found out that it is also a well know problem now in Leonbergers so told my Mum to tell the vet this as it is a very nasty disease. My Mum suggested this to the vet who shrugged it off but did ask the opinion of another vet who said it's not AF so assuming that the vet knows best my parents proceeded to have tests done etc, given antibiotics, cut open, stitched up, cut open stitched up, given steroids, taken of her Metacam that she has to her HD as it was apparently making her have blood in her faeces , they also suggested that she may have Colitis but never linked that fact that AF and colitis come pretty much as one but after some simple research I found this out and also the fact that blood appears in faeces as a result of the AF!
Well now after a year, Mum has to see another vet as her normal vet is away, she also (after I told Mum to) suggest AF again to this vet and the fact that it is common in Leo's, she was not sure about this and said she would look in to it. Well today she rings my Mum to say that it IS AF and that they needed to start her on drugs soon but the drugs needed are very costly - now the problem is that because this has gone on for so long the insurance will not pay out as its over a years treatment for the same area / thing! I am so angry because this could have been sorted at the beginning and the insurance would have paid for the treatment but instead my parents have to face the predicament that they are unlikely to be able to afford £500 per month so have to consider having her PTS as the drugs may not work anyway as the AF is so advanced. I have told my Mum to go back to the vets having a go etc but she seems to have given up the fight already. This is probably due to her GSD that she had to have PTS last year, yet again after the vets could not find out what was wrong with the dog for over and year as she became so skinny and lifeless the ended her fight....personally I would have seeked a second opinion but my parents were adamant that the vet was doing all she could but I have my doubts especially after this.
Sorry to whinge, I just had to get it of my chest as I am so angry - wishing that I had actually called the vets to make them test her for AF myslef!
Poor Cassy, she has suffered due to their ignorance / stupidity!