You would really have to define poor. If it’s just financially but he’s a hard-working individual, I would think that if they “click” then there could be some magic there with her help.
If he is poor because of substance abuse or drinking, while she might think she could marry and, “change him,” unless he’s very young there is a good chance he is already set in his ways and marriage would only aggravate the situation despite her best intentions to remedy it.
Always be careful when you marry someone, look at the big picture. If you can’t see the whole picture, don’t consider marriage until you do.