at my daughters wedding on saturday a mom with two girls had picked a dress for her younger daughter that was almost identical to the two main bridesmaids dresses, ie royal blue and high low hem, and my daughter was to say the least not impressed, and other people commented too, so if you are going to let her wear that dress put a cardigan over it to dress it down a bit, it also depends on what the bridesmaids will actually be wearing, if this is too similar just dont do it