You're in love with a girl and got thrown a little curve ball of, "oh, by the way, I'm a prostitute." I understand the need to find out more about her and her life but you should ask yourself why you want to know. If it's because you're now uncertain about the whole thing because she told you about her WG status, then knowing more isn't going to make you more comfortable in your original decision. If you're trying to decide if she's addicted to the business (many girls are) rather than just doing it out of necessity (again, many girls are) then this is probably a good thing to know. She could legitimately be one of those girls who got into it out of need, and have been stuck there ever since by a deadbeat family sucking up every dime she earns.
I'm not troubled by her query on your ability to support her family, per se. This is just part and parcel of the culture, and whoever in the family has the means is the one that usually pays for the parents, school for brothers and sisters, help starting new businesses, etc. You'd have to shoulder that same expectation whether you married a WG or a non-WG. As long as you're comfortable that she's not scamming you on the 30K HKD/month, and that it's legitimately what she's paying to support her family, then I don't see this request in anyway out of the ordinary.
However, as others have pointed out, most of us have the impression that these marriages tend to end badly. As far as I know, it's a subjective impression, not an objective one based on empirical, statistical data, so we could all be wrong. I would suggest that the fact that she's 42 would work in your favor for a successful marriage (in theory) as the only disaster marriages that I know about between gweilo's and asian girls have all been ones with very large age differences. A 50 year old bald, fat dude (see D'Artagnan's avatar
) marrying a 20-something hottie is going to have a harder time keeping it real than two mature adults who choose to marry: adding a huge age gap to a wide cultural difference in a marriage is just making things doubly hard.
Good luck in working through this. You are brave to try, and regardless of which choice you make, just be certain about it and don't look back.