So my I text my sister a few weeks ago and asked her if July 12th or 26th would be best for her for the shower. She text back that she was thinking September. I told her I would rather do it earlier so I had time to organize and shop for the things I didn't get and so I won't be miserably pregnant. I got no response.
She went on vacation and when she got back she called me to tell me about it. At the end of the conversation I said "So how about the last weekend in July for the shower?". "I don't see why you won't do it closer to your due date.". Once again I tell her about the organization and being able to enjoy myself without being ready to pop. "Well, I don't want to do that!"
Now I know this is getting long, but I need to pause for a little back story. Back in September she got married, and insisted that I throw her a shower and a bachelorette party. One on Saturday the other on Sunday, and both on the weekend I moved from Indiana to Kentucky. So not only did I have to deal with the stress and expense of moving to another state (without a job), I had the added stress and expense of giving her everything she wanted.
I reminded her of this by saying "Well I didn't want to throw you a shower on the weekend I moved but I did." Her response? "Your phone is breaking up and I don't wanna talk about this anymore." Then she hung up. I haven't heard from her since.
At first I thought I would just do it myself but I don't really want to. And you can't ask someone to throw you a shower, so what do I do? Sorry this is so long.

Re: Babyshower sister drama rant. Sorry, it's long.
I would either offer some middle ground - if not July and not September, how about August? If she says no, then I would thank her for the offer to throw a shower, and tell her you're really disappointed that it just can't happen.
Not everyone has a shower. It stinks, but it doesn't make preparing for baby impossible. ((Hugs)) I know this is super frustrating.
I would suggest trying to find a compromise in August. At least that's middle ground and would still give you time to shop and organise.
I'm due oct 23 and my shower is Sept 7. Anything we NEED to have if the baby were to arrive early we can buy ourselves, and if I was incredibly worried about the shower being too close to my EDD I would do just that. If your shower ends up being in Sept and you're incredibly worried about not having certain items, you may want to consider a similar approach. It's possible to provide the essential items for LO sans shower; lots of mothers do it.
TFMC 08.02.13 at 19+ weeks. Everyday I grieve for my little Olive.
I'm sorry that your sister is being difficult, but I think a late shower is probably better than no shower. Since she is hosting, I don't think there's much more that you can do. Good luck!
But you have to be ready to just say thanks but no thanks. It stinks but I agree with PP, a shower is a gift not a right.
TFMC 08.02.13 at 19+ weeks. Everyday I grieve for my little Olive.