I'm not sure that K12 will let her excel or catch up. When I spoke to them, the lady said it was basically ps online. IOW, no flexibility, no chance to accellerate classes.
I would recommend TWTM, because it outlines how to homeschool. FLL would be nice, if she can afford it. Then, and I really can't post this enough, search the library. There are resources there, really. Especially in the adult section, we live in podunk and our tiny little library has a decent section on hsing, afterschooling, supplementing, and then adult refreshers and education. All of those can be used. Also, if your state has Standards of Learning, she can use those to guide her. Here they are really specific. I've found them to be a good guide (especially for language skills and math) so I can tell if ds is at level or not, and what we need to cover so he meets the minimum requirements.