DH and I are both 22. Last year, he brought home about $15,000, where I brought home around $25,000. We split our necessary expenses ~50/50. That's housing, utilities, food, internet & phone bill. We keep separate bank accounts, and all personal spending (or savings) comes out of there.
Monthly, I have a surplus of 40-50% of my income, but currently DH is working part time and sometimes doesn't quite make ends meet. Even though it would be helpful to his pocketbook to split expenses 40/60 (or whatever), I don't want to be helpful to his pocket book. I want DH to be motivated to get a better job that he doesn't hate, and financial pressure is what I can provide. I don't want 15k/yr to be his acceptable income baseline.
I honestly think this depends on what the earnings are. "Fair" division of expenses, or the decision to combine incomes, is an incredibly personal decision. If you're talking about a situation where someone makes 50k/yr and someone else makes 75k/yr, it shouldn't even matter if the expenses are under control. In other words, if individual incomes are well over 25k-30k/yr, that should leave room for tons of savings (or spending) for both parties.
And though it wasn't clear, it sounded as if she wanted just small personal accounts, and that a lot of the money gets pooled together.
This is where DH and I will eventually end up (I think): Where the majority of income is pooled and saved or used to pay bills as needed, and a fixed allowance is moved to a personal account once a month ($50/mo per person?). Personal accounts are personal, and if she spends it all on clothes each month and you save yours up to buy a big ticket item next year, whatever. It's your personal money.
I'm just not willing to combine finances with a low wage earner. :) I'm afraid that it'll allow DH to relax and feel like things are ok, and not achieve more with his life. I don't want to be mooched off of. The downside to this is that I've got a fair amount of money saved, but my DH feels broke as balls all the time - because he is. It also means I have to foot big ticket items (such as car repairs) and ask DH to pay me back.
That being said, what I hear you saying is... "I'm not ready to/don't want to combine incomes, but she is/does." That's understandable, since that's basically marriage.
Do you guys plan to get married? If not, then you probably shouldn't have a joint bank account. If so, then everything is a shared pot.
Sorry if that was a bit rambling, I tried to bold the part that really matters! This has been on my might a lot lately too. Hopefully you guys can come to a good equilibrium/agreement for yourselves.