Yeah... no cute little sundresses with heels for football up in Ann Arbor.
She'll need Under Armour coldgear leggings to go under the jeans for November games. Brrr!!!! They are a tad pricey ($40-50 ish) but sooooo worth it. Saturdays in Ann Arbor are all about the game, even if Michigan has had a couple of unfortunate seasons.
Many Big 10 schools take their football as seriously as SEC schools do.
As to recs, since you are in the South, your sister might have an easier time getting them since it is common knowledge as to how important they are at many southern schools. So tell her to go ahead and get some, especially the ones from people who know her and can write a great, personalized rec. She shouldn't stress about them though. We are in Virginia, one of my kids goes to another Big 10 school. She got recs because well, that is what you do here. I think it gave her a leg up in some cases since not that many girls get recs at her school-the sororities were already aware of her when she went through recruitment, which is a good thing for a girl who was from out of state and didn't have hometown/school/camp affiliations.
Even though I root for anyone who plays Michigan, it is a great, great school academically and activities-wise, and Ann Arbor is a fun college town. I hope your sister has a great time there.