Bridesmaid BS in Ruby Woo

Hey ESB,

I'm looking for some advice - and just a bit of rant time let's be honest - about my sister bridesmaid.

So I'm getting married in about 6 weeks, but I've been planning for about a year now.
I asked my little sister to be my only bridesmaid... The reasoning of which eludes me now but I think it was just that it would be a nice, sisterly thing to do. No other bridesmaid but her - I'm not into the giant pack of women in matching dresses thing.

So my sister is the baby of the family and has always been a bit spoilt. She's about 7 years younger than me and the only other girl in my family. We weren't super friendly as teenagers - she has a wicked temper and we would have screaming matches about dumb things. But we've started getting on pretty well since she became an adult -- she sort of settled down and became more normal. We even went on a trip together.

My sister is wedding crazy - she has Pinterest boards, she loves decorating. I could see her as a wedding planner. But it also means that I think she's getting a bit carried away.

So far, I've been shopping with her and bought the dress she chose for herself. Not the colour or length I had in mind but it's her dress and I want her to be happy. She likes to self-tan while I'm a pale girl - I've always felt she looks too dark but I hold my tongue. She feels free to tell me that my flowers are crap (I'm arranging the flowers myself and posting trial run pics on Instagram); I'm hurt but I keep it to myself. She turns her nose up at our casual planned reception in a local country hall but I forge on (and hire some waiters). She wants us both to wear a flower crowns -- kind of not my style but it might look nice and she's excited, so what the hell?

But now, icing on the cake now, she's at me to hire a professional make-up artist for the wedding. No, I say. That's not my style. I want my make-up natural and I'm doing it myself. I'd like you to do it with me too, I say. We'll help each other.

So shit hits the fan. (Did I bring this on myself by being too accommodating previously??).
We have a massive argument that involves me being a selfish bitch because I know how much she likes make-up and she really wants to look perfect for the photos. Arguments about how I'm not a proper bride because proper brides get their hair and make-up done by professionals. She literally says "I know it's your day but I don't care! I want to look good for the photos so I'm deciding what I do!"

Anyhow, where to from here ESB? Dropping her as BM has been mooted but I think that would damage our relationship irrevocably. I'm loathe to give in to her though. I ask for one thing! We always look weird enough together because she's super tanned and I'm not - add her wearing full make-up and me looking plain.

Or do I keep the peace, let her go to the make-up artist on her own?

Ok give it to me straight...

Not a proper bride.

This bride is a mother f@cking C$nt!

This is a long story going back on over a decade of "friendship", so i'll try to summarize.  

"Ally" and I have been friends since we were about 10, we are now 25.  She has always been super controlling and, for lack of a better term, psycho when it comes to relationships of any kind.  We are complete opposites, she is super type A I am laid back, she always has a lot of people around her "friends" if you will, but they are in a constantly revolving door.  So much so that i can never keep straight who she is talking to and who she isn't.  I have 3 really close friends (not counting ally) and my sisters and thats it.  I do not need or want anymore.  For every event in her life, the world comes to a halt, because she is the only person who has ever had a birthday or graduated from school.  I indulged in this for years because I cared about her and our friendship and assumed the same of her.   When I got pregnant 5 years ago at the young age of 20 is when I started to see some disturbing things.  She got super pissed at me for not coming to her 21st birthday 2 hours away while I was 8 months pregnant! After I had my son I didn't answer her phone calls for like a week, I was tired and when i had time to talk i chose to sleep. Well i was bombarded by texts about how selfish i was for not answering. since then I have wanted to end our friendship, but the length of it and how close i am to her family as prevented me.  
that was 4 years ago and she still has not attempted to understand that my life has changed and her life is not on my list of priorities.  

She was a BM in my wedding last March and being the way that I am i pretty much did everything myself because I don't like to impose on people.  She had very little to do aside from getting a dress, which I let the bms all choose on their own as long as they were in the blush or champagne family. And attend a shower which I said to everyone if they couldn't make it was no big deal.  

She got engaged right before my wedding and she is getting married in November, in central america.  I'm MOH, i don't even like her anymore.  Like i don't want to be her friend.  When she told me when/where it was I said "that's so great! just to let you know though, we are going to start trying for a baby early next year so I want you to know there is a possibility I will not be able to attend."  She flipped her shit!!!! anyways i havent talked about that since,and the trying has begun so I might have an easy out anyways.  But in the interim I am being harrassed by daily e-mails phone calls and texts about every f-ing detail.  if i dont answer she goes crazy and berates me.  She is having a three day bachelorette party 6 hours away, she wants us all in central america for a WEEK of wedding celebration! WTF is she smoking?!  also on her wedding website there are lovely tidbits like "no excuses, there is plenty of time to save and plan for the wedding.." 

How do I break up with a friend of 15 years?  The wedding itself may be moot point anyways because of the impending pregnancy, but holy shit she is a nutcase and being a bride has made her even more unbearable. 

 MOH who doesn't give a flying f$ck about the wedding or the bride