12 year old daughter got a short haircut; stepmom-to-be is furious

I'm looking for an outside opinion on an issue. I have two daughters, ages 12 (from first marriage) and 2 (from fiance). I've been with the woman I am going to marry for 5 years now.For the past year or so, our oldest has been asking for a short haircut. My fiance has been adamantly opposed to this and has argued against it from a few different angles. She has said that a girl wanting to cut her hair short (like "boy length" short) might be a sign of mental unhealth, of wanting to "stand out" to an unhealthy degree, or of simply wanting to rebel. I'm fine with the haircut idea because to me it's just hair, but I've supported my fiance in this debate for the past year because she felt strongly about it and I didn't feel strongly either way. Our daughter feels just as strongly about it and has kept up her side of the argument saying often that she just wants a short haircut because she thinks it would be fun, and after all it's "her hair". It's been hotly debated for months.12yo is spending this Summer break at her biological mom's house. While away, bio-mom took 12yo to get her hair cut. It is now very short. Bio-mom sent me a pic which I shared with my fiance and how fiance is furious. We argued about it this morning; me arguing the "I just want everyone to be as happy as possible as often as possible and it's just a haircut it's no big deal" side, and my fiance arguing her usual points mentioned above. We were both getting ready for work so were unable to conclude the conversation, but agreed that we would have to after work.My question to you all..... how big a deal is this haircut? 12yo is a straight A student, not into drugs or sex, on Prozac for diagnosed depression after we caught her lying about talking to strangers on the internet and discovering she had dabbled in cutting herself, and otherwise just a normal kid. She finally got the haircut she wanted but had to do so basically behind our backs.Note about the bio-mom: she's within her rights to take 12yo to get a haircut. It's actually one of the details in our divorce decree that she is the tiebreaker vote in a situation like this, I think. She's been a bit absent due to moving about an hour away after we divorced, but 12yo still adores her and has even asked to go live with her. 12yo has said she doesn't want to live with me and fiance because it's too hard to live with fiance.Thanks, parents. Any perspective you can offer is appreciated. And just to be clear, I'm not asking for advice on dealing with either the fiance or bio-mom. I'm really just wanting opinions on how much a haircut really matters. via /r/Parenting https://ift.tt/2tKmfjo