Why would she friend request the unfriend me?

my brothers wife's maid on honor friend requested me on facebook before their wedding. I saw her at the shower and wedding and we got along fine (I am super shy and have trouble opening up). well at some point this year she unfriend me on facebook and I am wondering why. why would she friend request me then unfriend me? if she had soe sort of problem with me why not tell me? we seemed to get along ok with what little contact we had so its just weird why she would do that.