DIAGNOSE: a 21 year old girl who cannot establish boundaries in friendships; overly emotional; no motivation to work.

Codependancy sounds like a pretty good diagnosis. I would wonder what her childhood was like, and I'm betting she had difficulty establishing relationships then. My 5 year old niece has grown up most of her life without a mother, and she can be overly aggressive about establishing friendships and playing with other children. Obviously the other children don't like it, but she just doesn't get that she's putting the kids off.

No motivation to work comes from low self-esteem.

Disclaimer, I'm not a psychologist. I can see the co-dependency issues there, and I agree with mulder that this is Bi-Polar / Mania. I'm hypo-manic, and I go from high high's to low low's pretty regularly. She sounds like she's got a rough case of it.

Here's the clincher. You are not her doctor, you are her friend. It's a doctor's job to diagnose her, and to decide what the best treatment is for her, which is an important role.

It's your job to be there, to accept her for who and what she is, and to encourage her through that treatment, which is also an important role. Abide by it. If you need to understand how to better your role, go with this friend to a Depression/Bipolar Support Group and let the families of the similarly afflicted tell you what works for them.

Don't try too hard to understand. You can't understand. Just accept it for what it is, and love her the same way you would anyone.

If you start to have trouble being a roomie with her, don't force yourself to continue out of guilt. Honestly, that seems like a very nice gesture, but speaking for myself, I'd be insulted if someone was hurting themselves because they thought I couldn't get along without them doing so. If you are there for the right reasons, because you care, than stay, because that's the best thing this person can have.

Oh, and for the love of God, don't take her off the Prozac until you've gotten her to see a professional. Lithium is an often used choice to treat this disorder, but if she has meds, she needs to keep taking them until a psychiatrist says otherwise.

Get a new roomate. Its sweet of you to ty to understand her, but she appaears to bealot of drama in a can

The diagnosis is: you have a case of the NOSIES. She isn't going after people with a machete or dealing drugs out of your home, so give her a f'ckin break, pal. Or find a new roomie.

like my new crush said (blondebombshell), your roommate is a manic depressive case. idk if she's mild or worse because i'm not a psychiatrist (doctor who gives psy meds) but given that she is in prozac, i guess she's in the latter one. it's not your job to be there for her UNLESS, you are crazy altruistic or bffs with her. but if you are one of those who simply cares, be the guardian she really needs in such social situations since even if she does have an idea about how to go in a social meeting, her impulsive ad active nature might push other people away. try to be there for her, and guide her as she interacts with people. WARNING: this is a taxing job and can be considered as parenting level so if you're one of us mortals who can't bear such burden, i suggest you find some other roomie to room with. :D

prozac is not a solution to her situation, drugs alterates your brain and creates more imbalance than you had before
she needs to get help and good friends for psychological support

Get her off the prozac...

sounds like mania