It can get really dicey trying to divvy up money responsibilities, because people get into a "it's MY money!" instead of an "It's OUR money" mindset and start to resent you "taking away my money". Any time you start to get into that situation, back off because it is only going to get worse if you try to force it in that way.
What you have to do is make this a completely "logical" situation, not one that is emotional and possessive. You are two adults. Together you are responsible for your joint upkeep. So first, sit down and make a list of all of your joint expenses. Don't forget to include things that don't happen every month, like house tax and such. Break everything down so that you have a monthly amount for each item. Leave out personal pleasure items like "my weekly trip to the nail salon".
OK, now you can both agree that these things need to be paid. Now, since you are both mature adults, you both should pay your equal share of those amounts. It's not like she's an 8 year old that you are "caring for" - you both are working jobs, you both are earning income, you both have a responsibility towards your family expenses.
The question in here that couples decide on is, since few partners make the exact same amount, how to decide the percentage of bills each pays. One group of friends simply splits the pile in half. They figure that the person who made more also incurred more school loans and put in many more hours in schooling to get that money. The other person could *easily* have done that same amount of work and effort to get an equally good job. They chose not to. So to penalize the first person for working harder and making the effort is senseless. They each pay half and each spends the rest as they wish.
Note that in many of those couples it is the female who makes more, who got the better job. So it is NOT a male-female thing, it is a who-worked-harder-in-school thing.
Another option is to make an allowance for the person who earns less, if the *reason* they earn less is that they deliberately are doing so to help raise the family you two have. So say, in one case of one set of my friends, the husband stays home with the kids and makes zero while the wife works all day. The wife pays 100% of the bills. They are happy with that, because the husband is doing his "job" of caring for the kids. That is his contribution.
So in the same way, say the wife takes a job that only pays 60% of the husband's - but her job is very flexible and lets her meet the kids after school and take them to doctor appts and such. So while she only earns 60%, the other 40% in reality was "spent" on child-availability. So in that situation, the husband would pay a larger portion than she does.
So again, look at your two incomes, figure out what percentage they are of each other, and then discuss why they are different if they are different. And discuss what a fair division *percentage wise* of the bills would be. Again, you're not taking "her money" at this point. You are merely saying:
* Here is the total collection of family bills
* Here is the total collection of family income
* Here are the percentages available
Now that you have a percentage, simply break the bills into groups so that each person has the right amount to pay.
Hopefully if you present it to her in this manner, she will realize this is about two adults handling necessarily family payments. If even after this she is still clinging to "her money", it might be time to go in to a therapist. Most insurance policies cover it for free, and believe me, financial issues like this can completely destroy an otherwise happy relationship. It is VERY worth it to get this settled in a way you both understand and agree with, and is *fair*.