"She is not that rude like everyone in class avoids her."
This sentence might be confusing.
Initially reading this it seems to say that she, the subject, isn't very rude, AND everyone in class avoids her.
Using "like" in that position might indicate that you are showing an example of your previous point, which doesn't make sense here, because if she isn't very rude then there is no clear reason that everyone in class would avoid her.
"She is not so rude that everyone in class avoids her."
This sentence uses "so" and "that" to show cause. In this case "so" also modifies rude, to say that her rudeness is not very bad.
Breaking it down we can see how it works:
1) She is not
gives us the subject and turns the sentence negative
2) so rude that
this gives us a cause, and tells us we're talking about a level of rudeness that would cause something to happen
3) everyone in class avoids her
the effect of the rudeness
"So that" can be a very useful combination of words!