I think Grace was stupid and cowardly to do that and I cant stand her after doing that, I totally supported her up until she threw water

The fact is is that Grace kept convincing everyone she wasnt going to tolerate her and she didnt actually do anything to confront her, and when she did, she did it when she was leaving the house within seconds and Susie had no chance to retaliate (verbally) - typical cowardly behaviour if you ask me.
If its true that Imogen and Lisa encouraged Grace to do that then they were in the wrong as well.