Firstly, I'm not a mum, my mum suggested I post here for more opinions. It's hard to find a site of students who are actually any use 
I'm 23 and in my final year of a degree. I spent last year living abroad so a friend of mine said I could move into a student house with her and her other housemates when I came back. So I only knew 1 of the other 6 girls. Another one (I'll call her Lucy) is on my course as well but I wouldn't say I particularly knew her before because she never really comes to lectures.
This Lucy is the most difficult person I have ever lived with, to the point where I now cannot bear to go back to my house after Christmas holidays.
I can't even properly explain her. Firstly, she is a compulsive liar, but the lies change and I'm not sure whether she knows she's lying or whether she makes herself believe the lies. Can be anything as stupid as telling us all that she never eats breakfast when I know she cooks a massive fry up everyday before anyone wakes up (I go out jogging early and see her), to bigger lies. For example she told me someone had attempted to rape her in the summer. Then in December she broke down crying telling me she was pregnant since she was raped in the summer. I mentioned that she had told us all that he had attempted to rape her, and she said no, she had always said she was raped. (I don't want to sound heartless, my god if she's been raped that's horrific but from living with her I am inclined to disbelieve her, although would never tell her that!!)
The lies continue. She'll tell the other housemates she's been vomiting all day, when I have been in the house and know she isn't. Every few days she'll 'have been up vomiting all night'. When we suggest she go to the doctors because she's being sick she'll suddenly stop mentioning it.
Other types of things she does will be to come in the room and sit down on the floor and start sobbing (no tears!) because she's in pain from another fake illness.
She told us she had broken her arm, but the next day was playing tennis!
She practically never comes to university and always pretends to be ill so she doesn't have to come. She's told us it's because she's scared of speaking in front of other people, but I'm not sure if she genuinely has some sort of social phobia or whether it's that she wants the attention of us thinking she has a social phobia iyswim!
I don't think I'm doing a good job of explaining how odd she is. She's always going on and on about how much sex she has (why would I care?) but I know she doesn't have any, she lives in my house! Which is fine, but why lie? Problems escalate when she gets drunk and she will always make some sort of scene, then leave a note the next day along the lines of 'I'm the worst person ever I am so sorry you never have to see me again, I'll move out'. She stares at everyone, you can see her staring at you out of the corner of your eye but I have to bring myself to ignore it. It unnerves me though.
The thing is that I am not her friend, and I don't like her. But the other people I live with are friends with her, and they are aware that she is odd, but that's it...they just think she's a bit strange. I think she must have some sort of mental health issue because absolutely everything she does is simply bizarre (like filling my bedroom with bags and bags of rubbish). University are starting to question why she never goes in. I do feel sorry for her to some extent and definitely think she needs some help to help her regain a healthy state of mind. I don't really know what to do about it. I've suggested my other housemates take her to the doctors (they mention it to her and she agrees but no one ever helps her make an appointment), and I've even thought about contacting her personal tutor at uni. On the one hand it's not my issue, on the other, from a purely selfish point of view,- she's making my life so stressful, I'm sick of it!
Also my other housemates just ignore everything odd she does. Even if she does annoying or cruel things. We have to ignore. I am tired of ignoring her. She's making my time at university so stressful and I'm sick of all the drama. I go to university 8-8 everyday just so I don't have to see her. I don't think I should have to live like that. Also, if I were acting a bit odd I would hope that my friends would help me out, not just ignore my oddness!
What can I do?