Betty is a false myth in Grand Theft Auto IV.
Betty is a Dwarf Crocodile lost in the South Slopes Sewer in Broker, when Betty's owner left her in the bathtub. Betty, somehow, got flushed down in the Sewers. Betty's owner claims that everything happened in a glimpse of a moment, when Betty's owner left to listen to her/his mother's call and came back to see Betty gone. The user claims that Betty is four feet long and is a Dwarf Crocodile. Betty was bought from Vice City and, as myth hunters theorize, she probably was born in the Gator Keys before being sold by possibly Fudds Gifts in Downtown Vice City, but this is merely a speculation. Betty is still reported to roam in the sewers of South Slopes but myth hunters have never captured any evidence regarding her existence, but some claim to have heard noises.
This myth is simply false or a hoax, because Betty and his/her story wasn't mentioned in the game.