Part of this is her immaturity. The other part is she is in denial about this relationship, the last part is she sounds depressed.
You do know depression is not an excuse, it is a chemical imbalance in her brain. It is physical and needs to be addressed. When was the last time she had a full physical? I suggest she go to her doctor, get a physical and explain how depressed she is.. The aggression is a sign, the staying in her room is a sign and not being able to deal is a sign..
The more you try to "encourage her" to forget this guy, the more she will cling to him..
You need to have a sit down with your daughter and let her know you are "concerned about her". That she seems to be so unhappy and frustrated.
Ask her what is going on?..
Once she starts sharing.. explain that she is no longer a child. That her emotions are real, but as adults we sometimes have to step back and look at our lives in total. The plans we have, our living conditions, and the people that we depend on. Ask her how can you help her.
Remind her she is in college. She should try to place her energy into this. To start enjoying her time there. Ask her how you can help with this.
You also need to acknowledge the energy and length of time she has spent on this relationship, but that you are concerned because she seems so frustrated and unhappy. Ask how you can help with this.
Maybe suggest she make a list of the positive things about this relationship and the not so positive.. you can discuss it and then you need to think of at least 1 positive she has not included and THEN you can add to the not positive side of this..
THEN you can let her know what YOU need. You need her to quit taking her emotions out on the family. You need her to allow your home to be a calm place without all of the drama. Ask her to please try not to scream when she is frustrated or angry. It makes you feel uncomfortable or whatever words you want to use.. Do not use the words childish, do not dismiss her feelings for this guy, be very careful about not acknowledging her needs.
Becoming an adult, means we quit just thinking about ourselves. We want those around us to be happy. It makes us happy.
She should not need anyone else for her to be happy. She should be happy just with herself, before she can share that feeling with another person.
Try to convey this to her.
One more thing.. She is not a "girl", she is now a young lady or young woman..