You and the book are both right, except for your word order. It should be "Sandra is not as good a skier as her sister". You are not right about "such" always being followed by "that".
I have never seen such wonderful students.
Three blind mice.
Three blind mice.
See how they run.
See how they run.
They all ran after the farmer �s wife.
She cut off their tails with a carving knife.
Did you ever see such a sight in your life
As three blind mice?
Bruce