I'm not on birth control so what I'll say here is all what I've heard/read from others.
Yes, some birth control will kill your sex drive. So what she needs to do is go back to her doctors and talk to him/her about it. Change pills/patches/whatever. Try different doses.
What you need to understand is that pills/patches/etc change the hormanal balance in a woman. This can cause all sorts of problems like loss of sex drive, weight gain, over all change in attitude. It's not always good, and it's not always bad.
Theres a thread in the Ladies Lounge (you're more than welcome to look there, just don't post
) about a pill that supposedly increases sex drive. But it seems there are crazy side effects which your wife might not want.
But basically, she should get back to her doctor and try and figure out if there is anything that he/she can do about her lack of sex drive.