Weight is weight- split the food 1/3 for her and 2/3 for you. I know there's exceptions and some folks hike connected at the hip- but it's always a bad idea for any hiker not to carry any food, that's a "just in case" not to violate.
You can shuffle around the group gear if needed to keep her total lower- or better yet- you each carry a little heavy the first half of the trip and each benefit from eating the weight down.
Nothing wrong with doing a little hero hauling, but being a gentleman and all- in the name of equality mind you- each member should carry their fair share. That way you are both on the same pace and energy level, no point in you being all tuckered on day one and light and free on day six when you can both share those feelings equally.