What was your reaction to her response? You did apologize for being less than intuitive as far as when to bring the subject up didn't you? You got the opposite of what you wanted because she felt insulted. You didn't mean it to be hurtful but it was. Your best course now is to validate her pain and tell her your mistake was driven by your own pain.
I'm thinking the worst time to discuss sexual problems is right before or right after the act of sex. Bring it up when she is in the middle of something she is hating...mowing the grass or cleaning the kitchen. She might be more reecptive to the distraction then.
This is one of those things that happens when we fail to put ourselves in the shoes of the other person. You aren't bad for wanting to express your wishes to her but you still have things to learn about putting thought into how you broach the subject is going to cause her to feel. This was probably a lesson well learned.
So, what do you do next to try and dispell her feelings of inadequacies? Cathy