Is she asking you for advice or just offloading? Either way if your not comfortable being involved in the situation i would say so. Your wellbeing is important too so i would give her a list of helpline numbers if she wants them and make it very clear that you still want to be her friend and will be there to support her in other ways. I would rather someone say they weren't able to help me with a certain problem then just nod along and pretend their happy to listen or talk about it. Perhaps you could ask if she would be comfortable seeing a counsellor or someone similar? You could just explain that your worried for her wellbeing and that someone who is able to provide more professional support might be the best option for her. Good luck.