So that person whose fundraiser post you saw yesterday did end up raising enough money by the deadline. She’s going to be ok. That’s good.
You do not need to feel selfish or guilty for not donating your literal last $10 to her yesterday. Part of the reason that you didn’t have anything to donate to her yesterday is that you did donate to her last month, when her situation was less urgent. You also gave some money to other people who, like her, really needed it, even if their situations weren’t quite as dramatic. The fact that she’s ok now even though you didn’t give her your last $10 does not mean you sneakily got away with doing something selfish. It means that when you can afford to, you give people things, and when you can’t afford to, you can’t, and that’s ok.
(I get paid on Tuesday; I’m not in an emergency situation myself.)