That's not what fridging is- it refers to a specific type of death, where a female character is killed by a villain and left for the hero to find, specifically for the purpose of affecting the hero mentally. We don't know yet who killed Hermione and why, but it's possible that it was meant as a fridging.

TvTropes:

A character is killed off in a particularly gruesome manner and left to be found just to offend or insult someone, or to cause someone serious anguish. The usual victims are those who matter to the hero, specifically best buddies, love interests, and sidekicks.