Need Advice about Potential BM (long!)

First, I want to say that I feel myself slowly but surely becoming addicted to these boards!!

Now for my dilemma...I'd really appreciate any thoughts, advice, etc...

I want to officially ask my girls to be my bridesmaids pretty soon. For the most part, I am sure of who I am asking. There is one friend however that I am not sure about. We have been good friends for a long time - since high school. Although I consider her a good friend, I don't place her in the realm of 'BEST or CLOSEST' friend that I do the other friends I am asking. Significant periods of time can go by that we don't talk/email, etc. But other times, I'll talk to her a couple of times in a 1 - 2 week period. She can really be flaky at times and that's why frequently a lot of time will go by when I don't hear from her. She is like this with all her friends however, and the reason I am considering asking her is because I know that she considers me one of her best friends, although I do not consider her a BEST friend. I am pretty confident that if she were getting married, I would definitley be asked to be in her bridal party. And I am scared of hurting her if I do not ask her.
The other thing is that I am a little upset/disappointed with her right now because I got engaged 2 months ago and have hardly heard from her in those 2 months. She was one of those people I called the night we got engaged - we spoke, she was really happy for me - and then I didn't hear from her for like 3 weeks, and when she did finally call, it was bc she had extra tickets to a show and she needed someone to go with her. All of my other close friends had been like calling me every day - 'How is being engaged??', 'Has it hit you yet?' - those types of things. They sent cards, made a point to see me, etc. The first time I saw her was last week, 7 weeks after being engaged!! I think that is alot fo time...especially since we both live in the city, not far from each other!!!
I should mention however that she is currently in a long term relationship - and I know she is having some issues with not being engaged yet (they have been together longer than DF and I have), so I would not be suprised if me getting engaged has been hard on her.....BUT, not to sound selfish - what if their issues continue over the next year...will it effect her participation and excitement about being in MY wedding? I feel like I need people in my bridal party that I can rely on - one's that won't flake out on me - and with all my other friends, I feel that I can 100% count on them!
So....that is my dilemma. I do not know what to do!! I know I technically have some time before I have to ask them, but it's weighing on my mind what to do and I just want to make a decision!!!

Thanks for reading...sorry so long!!!
Any advice would be appreciated!
Thanks girls!!

I'd ask her to do a reading or some other honor. If she flakes out at the last minute someone can always fill in for her.

Explain to her that you wanted a smaller party but you still want to include her.

I am very happy that we decided to only have 2 people each. There hasn't been any problems. From what I've read on LIW, the people that you think may cause problems probably will and you don't need that stress.

My sis felt obligated to have someone in her party and the girl couldn't even get her dress hemmed.

I have a very similar friend situation to yours, and I've decided (although I still have a little time to change my mind) to not ask this somewhat flaky person. Not sure how many BMs you have already, but I already have 6, which was more than I wanted to begin with. So for the sake of trying to keep things more simple, I decided to not ask her, b/c I think ultimately there's a chance that she will make things more difficult than necessary for me and the other women in the party b/c of her flaky behavior. I think if you have doubts and concerns, it may be better to be safe and not ask her, just be prepared to have a solid and diplomatic explanation if she ever confronts you about it later.

Or, if you think it would work out OK, then maybe ask her whether she would like to be in the party and somehow tactfully bring up the issues that may be of concern to you, but in the guise of concern for her, not yourself. Like with my friend, I know money could be an issue, so I might say something like 'I would love to have you support me in the bridfal party, but I know you are trying to pay off debt/save money, so I don't want to put you in an awkward position...' or something to that effect, and put the ball in her court, with the issues on the table.

Oh yeah - that's the other thing....I already have 6 to begin with...she would be 7! I would rather have 6!!

I agree with the girls. Keep her involved in something small, like a reading.

You already know how she is, so don't fall into that fairytale thinking that people put aside their flaws when it's your day that's happening.... you're setting yourself up for a rude awakening, like I did.