so much the better
That is even better. I love your sister, so if she can come too, then so much the better.
so much the worse
That is even worse. If their policy ends up crippling the working class, then so much the worse for their chances at remaining in power after the next elections.
so much the
To that extent or degree, as in You decided to stay home? So much the better, for now we won't need a second car. This usage is always followed by a comparative adjective, such as better in the example. [Early 1200s]