Man I can only tell you what I would do........
Personally I couldn't handle it. I'm 100% against all narcotics and they have and will never have any part in my life. I would leave her. There's nothing left to say. Not only could her addiction get her killed, but she could very well wrap you into this and you could get in seriouse trouble with the police or her drug friends just by associating with her. I know this isn't what you want to hear, but this isn't what you need in your life. Once you are addicted, you will forever be an addict. No matter how long they go without their fix or how clean they stay, they will always have the itch.
Also if you are dead set on staying with her and helping her through this, I believe you are going the wrong way. As stated before I would leave her, however if you will not budge from her side then you must take action. You get her into a clinic and show no sympathy. You can't show sympathy to her AT ALL. Yes she may need you through this hard time in her life, however you don't need her addiction and she isn't willing to give it up for you. SHE ISN"T GIVING IT UP FOR YOU. As long as this last she will forever have the "addiction" excuse every time she goes on one a binge or lights it up RIGHT IN YOUR FACE. I"m not trying to be an ass or anything, but you have to be made aware.
As far as you should be concerned, she made the decision between you and crack when she went back to crack and left you. I truelly feel bad for you. I know how it feels to force yourself away from someone who you truelly love, but its something you MUST do. She chose crack Johnathan.......She chose crack over you.......
If you really wanna see someting that might help you, I recommend watching Requiem For A Dream . IT can be an eye opener. I wouldn't have sat here and wrote this if I didn't feel so strongly about it. This isn't your addiction, its her's. I pray that you do whats best for yourself man.......