Not read whole thread.
Tattoos seem to really split people down the middle for/against.
If it were my DD I would be saying this:
It will be there for your whole life - through your twenties, 30's, when (if) you have kids, through to later lafe, retirement, elderly and you're pottering around. You need to be sure that you want it forever.
And from that, get it somewhere that is not visible generally. Yes tattoos are becoming more mainstream but still visible tattoos (hands, face, poss ankles) are going to go down BADLY in many job interviews. I have a friend who is heavily tattooed in a trad industry and even in the height of summer she has to wear long sleeves and tights/trousers to cover, and can't wear her hair up. That's just how it is, at the moment.
If you're going to do it you need to get something that is meaningful to you which isn't going to feel wanky when you're older. Or something you like the pattern of. Following positioning / pattern due to fashion (I like cheryl cole's) is not the way forward. Be the person other people copy, not a sheep.
And at the end, I wanted a tattoo since 16 but didn't get one til about 26. I am now much older than that and still happy with it. I don't pay it any mind though, it's just a part of me. I am working up the courage to get another, quite sad and rather large tattoo right now
I don't regret it at all. Mostly they just become a part of what you look like, like a mole or a scar or something, just part of you. I don't know anyone who has ever wanted one removed (but lots who have lots).
There you go 
Maybe show her the thread?