I agree that since she is not in sports or any other school sponsored extracurricular activities, she needs to either get a job or start a full time volunteering schedule.
Also you need to have a conversation about your expectations of her behaviors, responsibilities and attitude. Her grades need to meet a standard, decide what that should be and what the consequences for her behaviors, attitudes and grades will be.
I always remind seniors that you may think you know what you are going to do once you graduate, but your senior year, making poor choices, taking dangerous chances and dangerous behaviors can ruin all of it.
We had a student in town who was drinking and driving and killed his best friend.
We had a student jump off of a side of a cliff after a night of partying.. He missed his original year of college.
And of course we all know the couples that the girl ends up pregnant her senior year. Changes all of their lives forever.
All of these kids had great futures ahead of them..
All of these were things that could have been avoided.
Give her more responsibilities,
you decide what will work to keep her on track and prepare her for college next fall.
She will need to start paying for her car insurance, her cell phone. If she wants a fancy laptop for college you will match her savings.
If she wants a car, she needs to come up with the down payment and the insurance.
Let her know you will only be able to give her $100. a month spending money while she is in college, so she needs to save up if she wants more, or if she wants to join a sorority, she will need to come up with the dues.. etc.
Prom you will give her $150. for the entire prom.. any more and she will need to pay the amount..
Whatever motivates her work on it..
I also strongly suggest you get the group f parents of the friends that your daughter hangs out with and meet with them and come up with the expectations and rules you are ALL going to enforce.
For instance in Texas, parents are not allowed to give any alcohol to any person under the age of 21, unless it is their own child..
If a party is held at your home and alcohol is made available to the underage, you will be arrested..
Of course no drugs can be tolerated and yes, weed is an illegal substance.
There needs to be a curfew. And parents need to keep in touch with each other about the parties gatherings etc.. and agree that nothing good ever happens after midnight.
We actually had a large group of moms, we would meet once a month and discuss, what was coming up for volunteer opportunity, money making events, etc.. with our children's senior year..
Here the snior class has to raise the money for their own prom, and their own Graduation night lock in.. They have to come up with the senior project.. etc.. and so the parents are the ones that are also supposed to help out.
It is a busy school year and the more you all work together, the more pairs of eyes and ears can help make it a safe year.
Invite the parents over for a meet and greet and talk about what is going on, and come up with some agreed communications.. email, cell phones, addresses.. etc..
Get on the same page, it makes all of you a stronger force with your children.