Well I am female so I disagree that the scenario of the Man taking charge always the case. I've known plenty of women who are the instigators... (although it is so in your case) Perhaps you and your wife can benefit from a sex therapist or a counselor if it is that bad? Sometimes it helps to get it all out... I currently am going to see one with my husband, our problem is different though, sex is very painful for me and I feel no pleasure even though I really love him. Also is your wife on any meds? Some meds kill sex drive, or there may be another medical issue... I have no idea since I do not know you and little info was provided.
And if I'm off the mark totally maybe she wants you to take charge and be the instigator of sex. Maybe once you are making love/having sex tell her exactly what you want... she should be willing to comply. The ball is in yoir court there... put her on top ...No matter what a frank conversation,though I guess you have already talked about this?... but a frank conversation with some of the harder things to say is waranted.
What is it exactly you are looking for? More spontaneous action? Creativity in bed? Surprise her maybe with a kama sutra book to try out? If you give a little more info I'm sure many people have ideas for you... how long have you guys been together? I think all couples go through rough patches.. especially if you guys have small children they drain you to where you just fall asleep once once your head hits that pillow.