Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.  The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.  Thus it is the challenge of competition among males of the species that facilitates aggression and violence.  Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.  The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males. 
Subscribe to The World's #1 Natural Fertility Website † Subscribe Now Proudly Supporting Fertility Resources
There are several relatively simple lifestyle changes a woman can make that might elevate T levels. Most obviously, if a woman believes her birth control pills are causing a problem and she feels she can adjust to a different type of birth control, she might stop using them (if indeed she's using them exclusively to prevent conception). She might also reevaluate her need for any of the various medications I mentioned, and perhaps seek alternatives that might not affect testosterone levels. For instance, there's some evidence that the antidepressant wellbutrin actually increases libido, but whether it helps the sex mojo through raising T levels or by some other mechanism isn't well understood.