animal lovers, what would you do?

The other day we were at my husband's dads house, and they have a female dog that's about 3 years olds. Not sure of the breed, but I think it's a lab/pit bull mix, Medium sized. Well anyway, I noticed something was hanging from the dog between her legs and didn't know what it was so I asked my husband's sister what was wrong. She said the dog has a prolapsed vagina. The dog didn't seem to be in too much pain but I could tell she was uncomfortable. She kept licking it and could barely sit. I felt so bad. My husband's two teenage nephews were laughing at the dog and I didn't think it was funny at all.  Well, later on I heard my husband's dad and husband's sister talking about putting the dog down just Becuase it has a prolapsed vagina, no other reason! The dog seems to be in good health. I feel so bad for that sweet, helpless dog!! My sis in law even talked to her boyfriend about "getting rid of the dog" by shooting it. I felt so bad. Why would they wanna do that?