Roommates!need help!

 I live with a friend of my sisters it seems like it's not working out tho. My roommate seems like she is going through depression, she has ALOT of feelings. She's very passive aggressive, needy, whiny and always has to have everything go her way.  She randomly tells me how she's so sad and just wants to cry, needs a bf ughhh at first i felt very bad and wanted to help but now it's so frustrating. I just wanna slap her and tell her to get it together, but of course in that exact moment she'll send a message telling me she's super depressed. She gets along with her family and has a chill job, I really don't understand what she's so sad about. At this point I don't even know how to talk to her... Sometimes I'm scared she might herself, Ive told her plenty of times if she needed to talk to let me know but nothing. I planned a vacation with her and now I'm super stressed out because she's constantly overthinking everything. I don't know what to say anymore to make her feel better, she's stressing me out and bringing me down now. What do I do!