This is a tricky situation. Your nephew found out not because she told him, but because he overheard some strangers' conversation and went online checking. I don't think something good could possibly come out of "hey, I found out online that you're doing porn - are you okay?"
I have a friend who was an escort for a few years. Although he started doing this back when he was a student, he didn't do it for the money - he's done different jobs before and had the opportunity to get something in another field or even ask one of his old bosses for one. He did it because he loved the job. He's never been ashamed of telling his friends about it neither why he loved it. This is a bit different because in escorting, sexual relationships are not always on the table and always coming from the escort, but in his case things ended up in the bed pretty often, because he wanted to.
Neither you or your nephew knows whywhy she decided to do this job.
Maybe it is indeed for the money, but maybe she had other motives. Maybe she even enjoys this career, in which case such conversation would only make you all uncomfortable. Which is why I would not advise you to confront her with her porn career. Maybe she simply does not need help with that.
However, if you want to find out if she does because you'd like to help her, maybe this is what you could talk about. You say your nephew and she were talking back in college, maybe he could reach out at her, ask how she's doing, what she's doing now or planning to do. If she expresses struggle and only if she does, maybe you could offer your help. But it is never someone else's call to decide whether a career choice is good for someone so, don't make it about it. Don't talk about it if she does not mention it first.
I don't question your will to help her - the world would be a better place if more people lended a hand more often - but, I think it's worth asking yourself: would I want to help her so badly had she not began a career in porn? I know there's a lot of stigma associated to that job and I don't doubt that many actors are unhappy with their jobs, but some people like it and knowingly chose it. I think it's important you figure this out before you try to help her because that information will help you help her the best you can.