OP, I don't think either of you are being unreasonable.
I actually didn't take your partner's response as manipulative. I just took it to mean that she was disappointed and upset because she's realised you have different values on something that might be important to her. She was probably crying because she's scared that if you do it, she'll lose her attraction towards you, and she doesn't want to feel that way. I think it's completely possible to love someone but for certain things to still be able to change the way you think/feel about them. How much just depends on how much it matters to her.
At the same time - it's YOUR body! Absolutely do whatever you please with it. Her take on it doesn't matter. It's just that she's communicated something that's true for her: "In the past, I've lost attraction over this kind of thing".
I've been in a similar situation on both sides.
My last ex liked to get Botox and other things done. It was a turn-off for me. But that's NOT because these things are weird. For me, it was reflective of a bigger compatibility issue - which was that she was very insecure, unhappy with her life overall, and quite obsessed with youth and beauty and materialism. I felt like... what happens when I'm 50, 60, 70? Will she find me repulsive? What about 35? 40? Will she be turned off by the lines on my face? It just made me uncomfortable. It just made me realise we were on different pages. I've just always liked natural ageing lines and stuff like that. I find it really attractive.
On the other hand, my ex before her hated tattoos and made it clear that if I got more than one, she'd have a problem with it. I understood, but got as many tattoos as I wanted anyway. It's my body. I don't regret it one bit.
At the end of the day, I think it's completely ok for a person to express what they do and don't find attractive. It would be way worse if they said nothing, you got something done, and then they aired their feelings after the fact.