So I got this friend who has a few issues and i think they could be serious problems. First off, I'll say that the majority of these (or maybe even all of them) are mental.

1. She is self-concious even though she's drop-dead gorgeous.

The girl is affraid to even swallow in front of people for fear that they'll hear it. Same goes for chewing.

2. She talks to herself and has imaginary friends even though she's 15 years old.

She thinks she can't really comfide in anyone because people always let her down, so she created people who she can always trust. I think she's got about 6.

3. She's becoming a pathological liar.

I know that she's lying. She gets more enthusiastic when she does it. She's made a whole imagery life for herself, filled with fake people and places and events that never even took place. I personally think it's maybe because she dowsn't do much. I mean, she's taller than most guys (especially when she wears her hells heels which is almost every day) ao guys are intimidated by her and don't ask her out, and she doesn't have very many friends. Most people so like her, but that doesn't mean they're besties.

4. She has anger issues and OCD (i think)

She never really has outbursts in school but sometimes when we talk about her homelife or whatever she gets this scary look on her face and tries to change the subject. I notice sometimes she has scratches all over her hands and arms and I am certain that they're self-inflicted. She told me. And about the OCD, it kinda goes into the self-image issues. She needs her lipgloss. OCD hasn't been diagnosed, but the way she uses it, I assume it is. She never lets it get thin (unless she's eating) and when she doesn't have it, she hypervenalates (know it's not spelled right) and cries, tgen bites her lips to "hide them from the world".

I'm just really worried about her. These things could evolve into worse things or lead to new problems. Advice?

Wow, this sounds like a friend I used to have. I a lot of this stuff happens during the teen years where you are testing your boundaries and hormones are floating around.
Have you talked to her, friend to friend, about your concerns? If not, I'd take her aside and have a nice friend day out. Do something together you both enjoy. When she is content, ask her about it nicely. Say you are worried about her and that you care a lot for her because she is your best friend. Try and get her to trust you. As for her imaginary world, try and get her into writing or drawing or roleplaying. It's the perfect way to escape the real world and not have it cross over.
In the end all you can do as a friend is make sure she knows that you can be trusted and that you care a lot for her.

wow, poor girl! :/ i think all these problems stem from low self esteem/self worth. you mentioned she is self concious but shes drop dead gorgeous, but then furthur down you say that guys dont ask her out because of how tall she is. im guessing the lack of interest from the opposite sex played a big part in forming her into the girl she is today. i can relate to an extent, as i am freakishly tall aswell, and skinny, so the amount of shitty jokes and wisecracks i have to put up with on a daily basis knows no bounds. i think the best approach you could take to this is not the old "friend to friend" talk, but instead you can just make an effort to make her feel more included, like in group activities/outings etc. try introducing her to some of your guy friends too. a relationship can work wonders to low self esteem. just try to make her feel more comfortable socially in general.

although a far better piece of advice in my opinion is to talk to her mother about it. maybe you can work out getting her to see a therapist of some sort. it would suck if me or anyone else on here gave you the wrong advice ( we arent exactly certified psychiatrics or anything) and you followed it, and she ended up seriously hurting herself. especially since you mentioned she already has cuts on her arms. anyways i wish you and her both good luck, keep us notified on the situation! :-)

This is sad, it actually kind of sounds like it could be Schizophrenia. Maybe not that severe, well, hopefully not, cause I wouldn't wish it on anybody! Low self esteem is certainly an issue. I have to agree with these other posters here, you should try to talk to her, but try to be subtle and nice about it, you wouldn't want her to get angry or upset. Just choose the words carefully.

Honestly I don't really know much to say too it, I fit some of that description, I have anger issues, and OCD and other mental issues, so I can relate. I wish you and her the best, hopefully you can help her... but at the very least, just being there for her is more than it sounds like most people do. I know for me, just knowing that there is even just one person you can count on, it means more than words can describe!! Good luck! :)