To add to Carl's list... did she recently change birth control medications?
Sometimes throughout use of one type of birth control hormone a woman's sex drive can peak then drop suddenly (or taper off)... other times, switching from one method to another can cause a sudden drop in sexual interest as well.
Hormones wreak havoc on a woman... at age 22, this would certainly be the more likely culprit.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen