Teenagers can be hard to deal with, even more so when you are not the parent because they seem to know how far to push you. The good news is you have a alternative that you can use to ensure her behavior changes. If you could give me some additional information I can help you with a game plan to get her in line and prevent the problems you are having.
Please explain and give as many details as you can:
What are the fights about?
What has she been doing that displeases you?
Whats her social life like? (Does she get to go out often, friends, movies etc)
Does she help out with any chores around the house?
Does she have a job? (Would you be opposed to her getting one)
What does she have as far as favorite possessions? (Such as car, cell phone, computer, etc)
Is she messing with any drugs or breaking any laws?
The biggest problem is she has went from no discipline to a normal household which is very hard for any child but more so for one who is so close to being a adult. Based on what you have told me it sounds like she does want to make a better life for herself but letting go of who she used to be is very hard. It sounds like she had no structure at home before moving in with you and what role models she had (Mom) was not a good model.
She wants what most any teenager has, and it is harder for her then a regular teenager because she can not have it. She is so close to being a adult to change her will not be easy. You have to sit down with your husband and determine what is best for your family as well as your sister. I am not going to lie to you.......sending her back is not a great idea. She will slide further into her mothers world and may never come back. But if you are to the point of doing harm to her you also must keep that in mind.
I do have some suggestions, I think you and your husband are going about wrong. You are treating her like a child, and thus she is acting like one. It sounds like she has had to grow up fast due to her mother raising her so the time for childish things needs to be put away. She is 17 and in just 1 short year she is a adult who must fend for herself if she can not follow basic rules. At this point someone must make her ready for that transition.
I would suggest sitting down with her and letting her know that you and her and your husband are going to have a adult conversation to deal with the problems that are present. Calmly (Without screaming or anger) firmly let her know that things must change and that everyone needs to come up with a game plan. The first step is to outline the rules of the home.........(Here are some examples)
Those are just some examples........when making up the rules try and be reasonable. She is still a child and as such will need some breathing room. Teens do have trouble controlling their anger so give and take. Let her know if she is angry or you are angry that she can go to her room for a hour to calm down before you discuss what is going on.
Structure is very important for a child her age........she needs some structure to ensure that her time is being spent in ways that are not getting her into trouble. She should have a set of chores that needs to be done everyday. Such as she has to do laundry or dinner dishes.
Is there a bus system near you? If so getting a job is key in helping to settle her down some. Taking a bus is not difficult and will help her learn to be independent. If not maybe you or your husband can drive her back and forth to work until she can get her license. 1/2 of her earning should be put into a savings account so she has something to fall back on when she is 18.
You or your husband may want to help her get a licenses as well. This is a big part of being a adult and something that will help her along the way. Structure such as chores, jobs and school are often enough to keep her busy enough that she will settle down. The key is to allow her freedom outside of this. On days off drop her off with her friends for a movie or time to just hang out. I know driving her around is not fun........but getting out and away from the family will give her space and make her less angry when she is home.
With every rule there must be a punshment........let her know that this is serious and you and your husband have had enough! Let her know that you understand she may slip some but if she continues on the same road you have no choice but to send her back. Let her know this is not what you want........but you also must ensure that she is not causing disruption in the family as well.
For some infractions you can remove her possessions.......let her know this during the conversation about the rules. Spell out how you will handle her behavior. Such as no computer for 1 week or losing the cell phone for a week.
At the end of the day if she really wants to change what you are asking is not to much.....but also understand that if you lose your temper it is only going to further the fires. Instead of getting into a screaming match send her to her room for 1 hour until you and she has calmed down. Never talk to her when you or she is angry otherwise it is going to blow up. Putting it off for a hour gives both of you time to calm down and think about the situation and come up with a idea on how to best handle it without fighting. Always talk to her like a adult......if you talk to her like a child she will act like one. If you want her to act like a adult you must treat her like one. Once you start talking to her like a adult she will in turn be less defensive and combative.
The drinking is a HUGE issue........and as such should not be ignored. Let her know this is and will not be accepted and even one infraction will result in immediate punishment of 1 month of no cell phone use or computer use. If she continues to do so you may want to consider speaking with her doctor about putting her in a rehab center for a few days.......while this may seem extreme she will learn very quickly that this is no fun and isn't worth it in the end.
Your main problem is the blow ups........if you can prevent them I definitely think that things can be cleaned up easily enough. The key is keeping control and never talking to her when you are both angry.
Your very welcome, I applaud what you are doing. Raising siblings is never easy and all to often people simple turn their heads because it is to hard. The good side is it sounds like you and your husband truly want what is best for her and she will see that and with a lot of work and a little luck you will get her grown and show your own children that family is always the most important aspect of life.
I wish you the best, XXXXX XXXXX you need anything please do not hesitate to contact me.