Honestly, not all women like to cook. I think that's an unfair stereotype that was placed onto the feminine head by the times of old - men working, women staying home being mothers and wives, and homemakers.
So perhaps the reason she gets offended is simply that she is not one of those who enjoy cooking, which would also explain why she sorta sucks at it. Like anything, it takes practice, and if someone just doesn't have the desire to do it, then the few times you may get her to - don't expect Filet Mignon topped with sauteyed onions, and garlic rosemary potatoes. NOT GUNNA HAPPEN, and if you complain she might just throw a bowl of cereal your way and call it good.
If she is just not a chef at heart, don't hound her about that, because that will make her feel like she is inadequate in your eyes, and she will get defensive. Making a joke about it probably isn't the best idea either because it could totally backfire on you and she could end up thinking that you are insensitive and relentless to the fact that this is something she is simply not talented in, and could become hurt by thinking that you are now making fun of her for it. (Even though it's easy for you to see how the joke could play out positively - you must always consider the possible havoc it could wreak also!).
I would say that if you are someone who really enjoys homemade meals, and cooking, and you would love it if your woman would cook for you - then you should take the initiative to look into simple but yummy recipes that you could - on your own! - could make for the two of you.
Why?
Because right now you are approaching this negatively, and in order to get results from any woman, you need to think outside the box and be able to demonstrate and deliver exactly what you hope to receive.
By you gettin off your rear, researching easy meals and going the extra mile to cook for her, you are not only showing her that cooking really isn't all that hard or anything to be intimidated by, but also that you are willing to get involved and put just as much into it as you are asking her to.
Pick a weekend to stay home and cook together, watch Food Network and learn some tricks, make it fun and light.
And you might be surprised to her reaction then.
Personally, I love cooking and since my step father is a Chef, I have learned a lot over the years. But you cannot expect every woman to be that 60s homemaker.
Here are a few sites with easy and fun recipes.
www.bettycrocker.com
www.foodnetwork.com