I would adise you to tread VERY carefully here. Pennsylvania has some of the toughest homeschool laws in the country (HSLDA has it on their watch list). If the school is saying they will issue her diploma, make sure you get that IN WRITING. In most states, homeschools act as private schools and are responsible for issuing diplomas (and in the vast majority of cases, public schools will NOT issue them for homeschoolers).
I have to wonder: if the school WILL issue her a diploma, why WON'T they issue her one now?
Start by checking the requirements in PA on the HSLDA website. If there aren't too many hoops to jump through, you'll need to determine WHAT to teach her, then HOW. To determine this, you need to know her interests and plans, as well as what type of learner she is (auditory, visual, kinesthetic).
There are plenty of homeschool curriculum to choose from - everything from curriculum-in-a-box programs (like Switched-On Schoolhouse from Alpha Omega) to computer-based courses (such as k12.com and Penn Foster). You can also design your own curriculum from sources like Rainbow Resource, Children's Books, Homeschool Supercenter, or Timberdoodles. Or you could go the unschool route and not use any real curriculum.
I would suggest hooking up with a local homeschool organization. They'll be up-to-date on what's available and what the state/local laws require. They are also an invaluable resource for materials, co-ops, support, teams, and everything else homeschool.