How do I tell my best friend that she shouldn't trust an old family friend?

My best friend’s cat is not eating but is going number 1 and number 2 normally. She took the cat to a vet who is also a very old family friend of theirs. The vet has told them that it is possible that the cat has Hep A.

Now this doctor’s reputation is very questionable as a majority of people in this city say he has killed/made worse their pets due to negligence or wrong diagnoses. He has now told my friend that her little tiny cat must get 5 shots a day for 5 days.

A similar thing happened to this friend’s dog just a month back where he was acting normal but would eat less. The vet diagnosed him with kidney stones and put him on intense treatment and the dog died within a week.

I am not at all comfortable with this doctor and think he’ll mis diagnose her cat in the same way and kill it! But if I tell her she will FLIP as her whole family trusts this person.

Help?