If I could say one thing it would be take sister up on her offer. DO IT! DO IT! DO IT! I have had 5 kids, so we've been through this many times. You could pump up your daughter by telling her this is gonna be her fun week coming up. See if your sister can plan some fun things to do w/your daughter, so she'll look forward to it. Maybe still plan to bring her over to see you all for an hour or two at a time throughout the week, and then "off to do something fun". Doesn't have to be anything big - a game, or craft, or kids meal and playground. Just tell her you all are gettin baby situated, so that you can spend equal time w/them in the long run and make things easier for all of you. Maybe have a surprise, ex. a toy, waiting for her when she comes home after the week w/your sister. She won't remember not being there w/you all when you come home from the hospital. Nor do i see it as alienating her. What you're doing is a huge adjustment the first couple weeks, and having her w/your sister will help you in making that adjustment. You and your husband will be "wiped out" when you get home, and it makes life so much easier knowing that your 2 yr. old is getting everything she needs w/your sister. You could even send your daughter some special "mail" at your sisters for her to know she is still really special to you all, and you are glad she's having fun, and can't wait to see her soon, and maybe (if you choose), you'll have a surprise waiting for her when she comes home. A specially wrapped "big sister" present.
My best wishes and prayers are w/you and your family through delivery and coming home. If you think about it or have the time, I would love to know how it turns out and/or what you decide. Take care!