Sometimes I donate, but usually I don't. I think that each person has to decide what is important to her and donate accordingly. To say that "not giving money (at the end of a semester, no less) isn't in line with the ideals of sisterhood and friendship" is ridiculous and immature. We all have priorities such as rent, utilities, loans, bills, etc. Sometimes charity takes a back seat. I wish I had money for everyone who asked, but I don't. Friends understand that, and they don't try to solicit contributions by questioning your friendship or sisterhood.
I made a decision a long time ago that I will only donate to a handful of legitimate charities because I know someone who raised a substantial amount of money for an organization that turned out to be fraudulent. Do your research if you want to make a donation. Make sure your hard earned money is going to a legitimate cause. I know that read like a PSA, but it is important to consider.