A replacement Sue is a Sue that takes the place of a canon character and pretends to be them. There were two of those in the mission that is to follow, but first, Tasmin breaks out the water works.
( oh god / Strawberry Lovin' )

Some characters are written deliberate out of character because the author doesn't like them. This is generally called character bashing. Sometimes it gets so bad it even seems the character was replaced by an imposter.
( Beware of Darkness )