My Mum [50F] is very upset/angry with me [20F] for letting my boyfriend [21M] cut my hair.

So my boyfriend and I had decided that we both wanted to cut our long hair short, and thought it would be a laugh to cut each other's.
Having never cut hair before, we were prepared for them to come out quite badly, but it actually went rather well and we're both happy with the results. All of my friends thought my super short hair looked cool, and they were impressed when I said my boyfriend had done it.
I sent a picture to my Mum and she completely freaked out. She said that she had tried for my whole life to ensure that I had "nice hair", and how could I let "some boy" chop it all off? She said that it "wasn't like me" and "I've changed", and that "no normal girl" would let a boy near her hair, and that all her female friends were horrified when she told them about it. She said that it shows that I'm "depressed" and clearly don't care about my appearance anymore. Then, she freaked out and started saying she was going to come and pick me up from Uni, so I wouldn't have to "walk around like that". I said that my friends all thought it looked fine, but apparently their opinions don't count because they're guys, and that every girl who saw would be horrified.
I tried to explain that I did it mainly as a fun spontaneous thing, and that I was happy with how it turned out so she didn't need to be upset about it. She continued to be really upset though and even started crying on the phone at one point, saying that I had completely changed as a person.
This is really worrying to me as I don't want to fall out with her over something so trivial as my hair! Is she over-reacting, or am I the crazy one here? What's the big deal?
Tl;dr - Bf cuts my hair, Mum hates it and says I've changed as a person


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