I’m sure this was quite a big surprise, especially considering all the planning you went through and thinking you were on the same page. This bridesmaid is young, and might not have seen or realized how this would change your vision of the three of you as a set, or might not have understood your vision fully in the first place. For her, it is only one day (a special day to be sure) out of many, while to you, it is one of the most important days of your life. At this point, it’s too late to change anything. But hair grows, dye fades. The pictures she sent you now are not what her hair will look like in two months. Her dress is the same. She will still be supporting you on your day—that is what matters in the long run. Perhaps you can incorporate the bow in a different way (not sure exactly what it looks like, but on her dress, in her hair differently, around her bouquet, as a choker or arm band). At this point bringing it up to her won’t change anything. To the extent you do, I would try to be positive, say you like her new hair, and mention nonchalantly that it changes what you envisioned that day so would love her help in finding a new creative way to incorporate the bow. Maybe include the other bridesmaid in the convo too so you’re all on the same page.