If Venus show up in this movie or the sequel, how you will react?

[Sumac]

Not liking her because she's a 5th turtle is a weak reason...there are far more reasons that make far more sense to hate her.

To the point where she shouldn't be even given any kind of second chance?

I think having only four Turtles is sacred

Nothing should be sacred in the story as long as changes have good execution.