We don't have kids in college, but as a perpetual student myself...
If you can't afford to help your sister, don't. She's a "Grown Up" now. If she can't (or doesn't want to) secure outside financing in the forms of scholarships, bursaries, loans, part-time jobs, etc, then she'll just have to reduce her course load or find another way to work it. I really don't think anyone is doing their dependants any favours by putting themselves in the poor house in order to pay for school and extras for said dependants.
re: books - this is actually one area where it is *really* easy to cut costs. You never need the newest edition. Ever. If things have changed radically from one edition to another, it is never over 500 pages, it's usually just a paragraph or two on a few pages. She can either read and take notes from a friend's book, or make photocopies, or speak with the teacher. I have never had a teacher who didn't offer up the use of their own text for a bit before or after class for those of us who had older editions and just needed to jot down a few things from the newer edition.
Rule #1 is never, ever, buy a book until the prof opens it in class/requires readings from it as homework. I didn't know about this rule in first year of my first degree, and I actually bought three different books that were never touched! Check the school and public libraries for books for english class, as well as for texts that are only going to be used for a portion of the semester. The library almost always has them, you just have to be a bit proactive to get to them first! Also, it is really, really rare that the entire reading list for a class changes from year to year, and people are always selling their books. Your sister won't fall irreperably behind if she waits two weeks to buy her books from the heaps of "for sale" flyers that will go up around campus. Especially in first year. And, lab equipment (if it's the typical glasses, coat, etc) can be found for much cheaper off campus. Thrift stores often have lab coats, and almost always have scrubs (get her to double check with the lab teacher - often they do allow a button up scrub or even men's dress shirt). Medical supply stores sell glasses and other equipment, typically cheaper than the campus stores.
Also, get her to check around town (the library bulletin boards and arts/indie newspapers are good starting points). In a campus town, there is often a lot of free stuff (meals!) going on. Food Not Bombs is the first one that comes to mind. A chance to get involved with the community while also getting a free meal once or twice a week.
Bla, bla. Sorry, you weren't even asking for advice, and here's a whole book of stuff! I hope you guys can strike a balance that works for everyone.