What does the phrase “the scalding humor that erupted like bubbles in lye” suggest about dee?

This phrase suggests Dee is an abrasive, antagonistic character. 

Walker makes this clear through this brief description of Dee. "Scalding" implies burning or blistering -- something hot and painful. "Lye" is a solution used for cleaning, one that causes painful burns if touched.

This brief description truly summarizes Dee's character: angry, abrasive, and antagonistic to her others, especially her family.