Friend finding things difficult to move on

My friend and I share an office, we are both very studious and have lots and lots of work to do. The problem is, we keep getting a visitor...

A mutual friend of ours, who we love dearly, was meant to leave our place of work a long time ago. But she is finding it extremely difficult to let go. Her things are still in our office (she says she has no space at home to keep stuff), and she finds excuse after excuse to come in. She just sits in our office reading, or sorting through papers (by strewing them all over the floor) and, quite distractingly, engaging us in conversation.

She is on anti-depressants and is seeing a psychiatrist for depression. She has little motivation to go out and find a permanent job, relying on part time positions just to see her through. She also takes offence really easily... we dont want to hurt her and dont know what to say to her. We dont have time to sit around drinking coffee and nattering about things that are not our priority. Stuck!!

Any help much appreciated :)