Are you interested in her? 
I can understand your concern for a friend, but please remember to
be tactful. Here's why:
1) Should you go too far out just to help her, little wonders what
she'll be thinking abt. 
She can
either think that you're eating sour grapes, thus trying so hard to
discourage her from a r/s she thinks is wonderful, OR she will appreciate your concern for her and hopefully
wised up.
2) Should you let her be on her own and s.h.i.t. happens, then on
your side, I think you'll feel bad for not trying any harder to
dissuade her from what you think is bad. On her side, you'll be
accused of not trying any harder to dissuade her from getting
herself into this unwise r/s.
3) Should things work wonderfully between the two of them,
YOU will be yet accused of trying to break up what
seems to be a wonderful r/s *keeping my fingers crossed that it
indeed will be wonderful*
Ultimately at the end of the day, you don't really stand to gain.
I'm not trying to discourage you from helping your friend. But
girls at this age tend to be naive and easily coaxed with sweet
nothings. For her, at this moment at least, I guessed she's more
into that guy's word than yours. Definitely don't wish to see the
day when she comes back barking at you for either helping too much
or too little.
Take heart, it's not your responsibility to make sure s.h.i.t.
don't happen to this friend. She should be responsible for her own
life, her own actions. Some ppl learn things the hard way. You can
do this much as a friend, for a friend.
cheerz..
