Verbal abuse, emotional abuse, and mental abuse are all forms of abuse. If she is verbally (and most likely emotionally, as those two things usually coexist) abusive she is an abusive person.
Now, should the WCA get involved? No. This purpose of the WCA is not to impede on private lives. The only thing they can really do is ban Yiheng for... being a victim? What the WCA should act on is David Epstein's wicked behavior. While David's behavior may very well be a result of a broken/abusive household, as is often the cause of his behavior, it is no justification to abuse others and make racist and ageist comments. I could go on but this is obviously a very different matter.