tired of being labelled the bitch

I should be studying and preparing for what may actually be my last two weeks as a student in coursework (I say may actually be, because it was recently suggested to me that I take some undergraduate courses... although I understood the reasoning for such a statement, I feel very uneasy about being the process of attaining my Ph.D. and enrolling in a undergraduate course, especially when often times I could be handed the textbook, be told to read it, and then teach the class.... hopefully I can just read the textbook!).....
I started to multi-task however.
There is a movie on t.v. tonight entitled "The 'R' word". It may actually be more of a documentary type viewing. My mom has to take my sister bowling tonight so she will not be home to view it and asked if I could do so for her. Of course I can!
The sometimes non-productive part about multi-tasking is that the focus that should be placed on the primary task, studying, becomes completely abandoned. This is what occurred moments a go.
So the movie on t.v. is about the difficulties some individuals and their families have faced when one has a disability.
Obviously, sometimes I can relate.

This weekend I was home. I took a shift at the bank on Friday - and ended up staying at my mom's longer than intended do to a horrible headache that had me seeing spots when I stood (therefore probably not a smart decision to drive).
My mom also happened to be working this weekend so in the end it was helpful to her that I stayed so that someone was around for my sister.
My sister probably was not even aware I was home as she spent almost every waking moment on the telephone. Meh - if that is what she wants to do, thats fine with me. I had a headache anyway and couldn't exactly convince her to get off the phone to go for a walk if I couldn't get off the couch myself.

The part about the relationship between me and my sister that truly bothers me - is that I get labelled as the bitch. I do. I honestly try to be a good person in life - but every time I go home I get reminded of just how horrible of a person I am.
I'd like to argue this point for a moment.
Although I don't disagree that the label I have been given as the "bitch of the family" is not uncalled for - I do not feel it is just.
My mom for years has told me about how she has just given up - how she has no fight left in her and it is just easier to give in because her fighting doesn't seem to make a difference any way.
One issue with my sister is her craftiness for lying.
I catch her in lies all the time.
I'll ask her if she just lied to me and she will swear she hasn't.
She learned that if she said "I'm not lying" that people backed off and believed her. Well that stopped working so now she's saying "I'm being honest" or "I'm telling the truth, why don't you believe me". She tried these on me this weekend, and I laughed calling her bullshit. I'll sit down with her and walk her through the steps... and by the last step she has admitted that the first one was a lie... "but she didn't mean to lie" <-- thats the newest she drafted this weekend!
Every time she gets caught though - she starts crying.
Which of course makes me feel like a horrible person - but wait a second - I am not the one that lied - and she lies about the silliest things - and I explain to her every time that I just need to know the information - if she just tells me the truth to begin with then she won't get in any trouble. Its not the information I get upset over, it is the fact that she lies. And every time she tells me she understands - and I know she does - she is a lot smarter than people give her credit for - and meknowing this and not putting up with her crap is what influences people thinking I'm such a bitch.
Anyway - so the part that bothers me - is that I shouldn't have to be labelled the bitch - but I feel like I'm actually the only person who gives a flying f$#k .. and as a result I am the bitch. My mom just gives up - unless I pretty much give my mom a lecture about how this is not acceptable behaviour for my sister.. and my mom then goes and talks with my sister.
WHY AM I THE PARENT?
Thats my issue.
I am the YOUNGEST in this family - yet have to always shoulder all the crap that goes on - and I get put down and ragged upon every step of the way. I'm the bitch. I'm the irresponsibly child who denies real life expectations by staying in school so I can "party more". I'm the greedy one. I'm the one with the attitude problem.
Maybe I am bitch. Maybe I do have an attitude problem. But maybe - just maybe I'm the only one who gives a damn to put up a fight for this family. I've been a told a few times that I'm the rock that holds things together in the family - but two seconds later get criticized for doing so.

I'm getting tired. I just want to be the sister, the daughter. I don't want to have to explain to my older sister why her actions are wrong. I don't want to be the one my sister is fearful of because I'm the only one who will discipline her - because she knows her tricks don't work on me.

I know my sisters time is limited - so why don't I get to enjoy time with her? When she passes I'm going to feel SO GUILTY that I didn't spend enough time being her sister. Every time I go home I keep this in mind - but it doesn't take long until she does something unacceptable and I try to let it slide - but then she just keeps pressing to see how much she can get away with.... and I just can't let her rule the world like that... and I get that I could totally be wrong and I should just let her go wild... because its harmless right? Unfortunately not everything she does is harmless...

And now I feel so guilty for wanting people to understand my position. I know that my sister has a ridiculously hard hand dealt to her in life - and I really have nothing to complain about in life - I have been so ridiculously blessed - but I have to tell you - I'm really tired.