What do you mean why ? girls carrying condoms in their bags its pretty common when they are young or in their prime (20/40 years old), its always better to be cautious about those things one never knows when you might need it. Also if you are sexually active its even more common, even if her mother was not married anymore, that doesn't mean she is single or looking for a couple or a fling here and there anymore, remember adults do have life after all, or do you now imagine yourself having sex with someone you like in your 30/40+ anymore?