I kind of see what everyone is saying here. It is a hard situation because ultimately it IS her choice. If she doesnt give a crap about what you think about it though that is also a problem..

See, i went through this with my ex.. Which i apologise for my b*tchy first response it just kind of reminded me of him..
I really wanted this beautiful tattoo, lillies and a quote that symbolized my love and guilt for my unborn baby that i lost last year. It meant a hell of a lot to me, and i waited months after the incident to make sure it was something i could live with. Almost a year went by and my friends dad is a tattoo artist, he said while he was in town he would do the tattoo for a great price. Obviously i went to inform my boyfriend about it.. He knew the whole situation killed me and i think he knew how much this tattoo would make me proud. But he said 'eww, a tattoo that big is going to look manly and i wouldnt be attracted to you looking like that.'
I was pretty upset, he knew how much it meant to me and how happy i would be with it. Yet, he was shutting me down saying no to getting it. Obviously with him saying he wouldnt like it and it would 'turn him off' i turned down the offer from my friends dad and never got it done.
Now it just makes me SO mad i listened to him!! Like, its my body why the hell should i listen to him putting me down about something that made me happy right? See my point here? She might be thinking.. 'This is me, he should love me for me and my decisions and what makes me happy'.

But, in your case she doesnt realllly seem like she gives a crap that you may not like it.. As she obviously isnt going to take notice of what you say.
Its a complete compromise here, you are going to have to respect her wishes that this is what makes her happy and you be happy for her.. And she will have to slow it down a notch and take notice of what you think and feel about the tattoos and maybe get something that you like?
Pick something out together that you both like, something that means something and that you will both like on her body?