Did someone mention me? I knew that I was supposed to abandon mopping the floor and get onto the DIS for some reason.
I'm homeschooling my 17 year old BIL as a junior this year. We pieced our curriculum together from various text book companies. I know that some people like to order from one company, but that just doesn't work for us. I want the freedom to get the books that will be best for him in each subject.
I'd start with
HSLDA to find the laws and other important things about your state. The link I gave you will list the ways that you can legally homeschool in California, and it also has a link for homeschooling groups in your area. You will see stories in the news about how it's illegal to homeschool in CA. That is absolutely, completely and totally false. You can homeschool. You just need to follow one of the legal alternatives allowed in your state.
The first thing I would do in your shoes is try to see if there's a curriculum book fair in your area any time soon. Most of them are during the summer, so you may have a hard time finding one, but you may get lucky. Do that first because they'll become more and more scarce as the school year progresses.
Then contact some local homeschoolers. Find out how other people in your area homeschool their high schoolers. Ask other parents what has worked for them. You will find some people who have homeschooled high schoolers. It's not as common, but the people are out there. The main problem is that they frequently don't attend support groups because they've been doing it so long. So ask people if they know anyone. You will find some families who do it, and they'll probably be willing to help you.
Some of the book vendors have mini shows in hotels somewhat fequently. I know A Beka does. Look into that.
Check out the Big Book of Home Learning (or something like that) by Mary Pride. I think that Vol. 3 deals with highschool curriculums. Volume 1 deals with packaged curriculums. It's written from a Christian perspective. I don't know anything about your religious affiliation, but it's a good book even if you don't want Christian materials because she does evaluate some secular stuff.
The Elijah Company is a great source for homeschooling materials. They only sell stuff that they've carefully evaluated and like. They also have wonderful articles.
There are lots of message boards, similar to this one, that deal with homeschooling. Sample a few and find one you like. I like
Homeschool Christian, but there are lots of other ones.
Finally, about it being your step-daughter. You may run into some problems there. We're in the process of becoming my BIL's legal guardians right now because you have to be a legal guardian to homeschool in this state. I know that your DH is her legal guardian, but in the group that I'm joining, the person who does 51% or more of the teaching has to be the child's legal guardian, and you have to join an accountability group in SC to legally homeschool. So you will need to see if that's going to be a problem. There will be ways to get around it if it is, but you'll want to tackle it right away if necessary.
Good luck! Let me know if there's any way I can help you. I haven't been doing this long, but I know what it's like to just jump right in during high school. It's a lot of work, but it's very rewarding.