I'd also like to offer a piece of advice, please learn this the easy way as i learnt it the hard way, and i'm still ill because of it.
You are not responsible for your friend (Sara). Infact, you are not responsible for anyone but yourself. I know that is hard to take and i know that you feel that things are just hanging on because you're still in there (plugging her boat) but i promise that you cannot do this for too long.
I had to learn a hard lesson of loving myself, which i thought was the most selfish thing i could ever do. I've been proved its not. "Do to your neighbour as you would have done to you" is not just telling you to look out for your friend, but also to look out for yourself in the same way. Do not neglect yourself or else you will be no help to any of your friends. Always put your relationship with Jesus before your ministry (helping your friend). I never used to distinguish between these things, so used to spend hours on the phone to people who needed help, and ended up so exhausted i was reading my Bible as an afterthought at the end of the day when my eyes were closing, and thought that the phone calls were the same as sitting in His presence for half an hour. Its not, and you need God as much as your friend does.
I promise that if you lift the situation up to Him, God will not only plug her boat but lay her boat in his palm and lift it up Himself. I understand that letting this weight go will seem impossible, but please give it a go. Don't even hang on to a little bit, you need to swim free. I don't mean that you should love your friend any less, but just to understand that as a human you have no power over her or her decisions. It is only God who can do that, so I pray that He's on her case right now.
If i've got the wrong end of the stick or way overstepped the mark, post up again to let me know, or your welcome to PM me, my box is always open and i'll read it. I hope things get better, i've been in your situation and i know how painful it can be to watch a friend as you have to. I pray also for peace in your heart.
Blessings,
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