Well first of all, don't give money to people who stake out regular territories. They are the ones most likely to not actually need help. However there are thousands if not millions of people in the US that are in dire need.

What I find to be almost as bad as this girl are the foundations for helping the homeless that 90% of what you give to them goes to their employees and infrastructure.

And that includes all those telemarketing chartiy places that sell you lightbulbs and stuff over the phone, like Salvation Army.