I think this is an issue that you need to talk with her about. I find the best way to start out a conversation is to say "Hey, Hun. I have a problem I need your help with." (Works for just about every situation, telling someone you need their help)
I am a 42 year old woman who never had a sex drive until about 36 years old. Then it was on like a light switch. My husband and I go through spells of inactivity (usually when there are stressful times) One of will talk to the other and we make sure to have a date night and relax.
One thing you should definetly do is have some blood work to rule out hormone imbalance. Try to relax and let it come easy. There is no rule of when you have to feel like it. Good luck!