Well, when I was 18 I was deeply in love with this girl. We where sure we would last a life time etc etc. After 1.5 years she broke up with me over a text, and said we should be friends.. We even tried that, and after 6 months of trying to be friends I can't stand the bitch.
I'm now 22 years old, and she's still trying to get in contact with me. And this is the girl I loved of all my heart and all that, now... meh that dumb girl is long gone. Glad I didn't get a ink of her or anything, would fit with the other "great" ideas I had back then.
So no, don't get a tattoo for a friend. She's out of your life in a couple of years. You'll end up with someone special, and BOOM no more time to hang with that girl.. or the other way around.
It's so many other cool stuff you can get a tattoo of. Like me: I'm working on a bad ass pirat tattoo sleeve, traveling around and getting ink in different countries. A sleeve of memories for sure. My other one is not that well tought trough and, in my opinion now - dosnt seem to fit together... I started on that one when I was young and stupid.