Parent's Advice - Twitter/Facebook

Hoping for a parent's perspective on this situation:

DH's cousin - female, 14 years old is very active on Facebook and Twitter. Her mom is on facebook and she friend requested the entire family. Her facebook posts are pretty tame, silly kid type of things. Although a few things have surprised me (wouldn't want my daughter to post those things, but not too bad).

Her parents are not very internet savvy and I don't believe they even know/understand Twitter. SIL and BIL both follow her on Twitter and she follows them - she is aware they have access to her tweets.

Lately, her posts have gone from bad to worse - things like drinking, smoking weed, hooking up with boys (wish I remembered his name) - things like that.

She has her real name (not that common of a name) as her screen name.

I am worried on a few fronts:
1. is she really doing these things?
2. Posting about drinking/weed, etc. that is illegal could get her into real trouble at school or with police
3. Using her real name is so foolish - any future employer (i.e. internship, etc.) will find these tweets. Less of a concern right now but would want her to learn this lesson before it "matters"

I think we have an obligation to tell her parents - Opinions? Guidance? Advice?

Re: Parent's Advice - Twitter/Facebook

I totally tell my siblings about my teenage nephew's inappropriate postings. Most of the time they are aware of it as they do monitor them but yes, as aunts I feel we do have a responsibility of guiding them. It's not tattling at all. I am the cool aunt for many many reasons. And I want my nephews to be good kids. One of which is my Godson whom I've made a vow to guide. Not that they post inappropriate things often if ever but I've caught a few things.

I do not know what the times will be like when DS is remotely near ready but I'm going to keep him off the Internet as long as I can and when the day does come, I'll be all over monitoring his presence and representation of our family.