Let's take each of your questions in turn:
...upon discovering this evidence which confirms our suspicions, should we confront her with our findings?
>>>>>>>>>>>>>> Yes ...the strategy you may want to use to go about this is in the Online Version of the eBook: http://www.myoutofcontrolteen.com/q-a
Should her absentee parents be contacted before we confront her?
>>>>>>>>>> Not necessarily, but it might be the polite thing to do to keep them in the loop. Maybe wait until after you confront your granddaughter to update them. Also, I think it would be better NOT to invite the absentee parents to the confrontation.
Should we be contacting some outside intervention for her as well?
>>>>>>>>>>>>> Not yet.
1. Re: possession of alcohol: use the strategy in the link above
2. Re: lying: this is covered here: http://www.myoutofcontrolteen.com/lying
3. Re: sneaking out: refer to the section "What to do when you want something from your kid" in this chapter: http://www.myoutofcontrolteen.com/am
4. Re: smoking: this is covered here: http://www.myoutofcontrolteen.com/q-a
under this headline --"I'm pretty sure my daughter is smoking cigarettes. I hate the thought that she is doing this to herself, especially at such a young age. Any ideas?"
5. Re: hates my husband & myself: She doesn't hate you, rather she loves you but is angry with you -- and this anger (which is really about her parents) gets misdirected toward you. Thus be patient with her and let her have her anger -- she will not be talked out of it. (Notice I said "be patient" rather than "you should feel sorry for her and over-indulge her to compensate for the bad cards she has been dealt").
Keep me posted.
Here's to a better home environment,