Im a quote-collector, and one of the things i've done in the past when i've wanted to be there for someone is a book of quotes. It's really simple, just make a little book (i like to use different coloured pieces of paper in the same size) and fill it with appropriate quotes for the occasion. u cud put some in on sisters, graduation, pride, love. there are about six bajillion sites online with quotes. all really easy to navigate.
feel better!! i'm sure ur sister understands.