I'm a dude, but
http://en.wikipedia.org/wiki/Ages_of...rthern_Ireland
It's totally legal in Northern Ireland. I generally follow the 1/2 age + 7 rule, but being 22 that can be the difference between a high schooler and somebody that has their sh*t together. But ultimately age is only a number. I've known a 21 year old to date somebody 30 years his senior (a gay couple, but still).
I will say, 17 year olds universally still have a LOT of growing up and changing to do, and she likely won't be the same person say, 5 years from now, or even sooner.