Is her situation with having a child much different from Victoria's (MC's mom) situation in the past or Lucy's situation in the present?
We don't know the details, so it's difficult to say how their individual circumstances differ. It's however worth nothing that Lucy didn't join the club because she was lacking money. She did it because she wanted her kid admitted to prestigious school and the club could apparently provide her with this as reward for winning the contest.
Also keep in mind that even with Victoria and Lucy in the picture, that's two single moms out of how many women with poor jobs raising their kids single-handedly? It's not some automatic slide to prostitution by any stretch.
edit: Also also, if you're going to bring up Victoria then let's not forget Victoria isn't currently making porn videos. She's stopped at some point, and likely quite a long time ago. And i doubt this was because she couldn't get any further roles.
And how getting fucked by a number of strangers during the Exhibition is different from prostitution? Oh yeah, instead of getting small sums of money from each client she hopes to get one large sum of money at the end (still being fucked by many strangers in the process). Different indeed
That there is no difference is very much the point. Rose didn't prostitute herself until she was backed into the corner by loan sharks. Once this problem is resolved, why do you think she'd do the same thing she didn't do when she didn't have to (i.e. prostitution) when she no longer has to?
The only argument for that you've suggested was "it's better money" but as pointed out Rose
normally didn't care about getting more money to the point of earning it with her ass.