My sister is 14 going on 30. She thinks she knows everything and right now she is boy crazy (for older boys... like 16, 17) She's going to be a freshman this year and I don't trsut the boys in school. Should I keep and eye on her even though she treats me like dirt on her shoe? My mom never seems to punish her, and my dad isn't around so I feel like I should say something to her but every time I do it just turns into a fight. She doesn't want to listen to anything except her loser friends. I try to leave her be but its hard, I don't want to see her fall.
Should I keep giving her advice or no?
Should I keep and eye on her?

Keep an eye out, but don't interfere unless you are sure she's heading for trouble.

Sounds like she is not going to listen to anything you say and fact is she could very likely do the opposite of whatever you say just for spite. I wouldn't say anything but keep an eye on her so that if you do see her headed for serious danger hopefully you can find a way to intervene but for now she is going to learn the hard way and eventually wake up to realize you can be a help.

(I may not have a very popular answer... ) And I agree w/ both nohelp4u and scottgem. My feeling is that she's really getting some deep seeded reward for her actions and lifestyle. She's not going to stop it any time soon whether you like it or not. She's going to play this out... This is who she wants to be. She's young and in the midst of trying on a lot of "hats", (personalities. This helps her discover who she is... ). I would, for sure keep an eye on her. That's only looking out for someone you love and that's very loving of you. I would, however talk to her about getting herself on birth control or buying condoms if she is going to be dating boys that are already having sex. A lot of girls from "broken homes" begin to replace their father figures w/ boyfriends. In fact it becomes their LEADING REASON TO LIVE. She needs to be protected from consequences that can arise when dating boys that are older and sexually active. If you need to plop some condoms on her bed... in the hopes that your message becomes clear, then do it. You can't stop her. You can only help protect her from STD's and pregnancy. Also, instead of acting like a mother/father... try acting like a friend. Be there for her and try not to judge her. She'll pull away if she feels judged. Being right is NOT more important that being THERE...