Yeah I don't think I'd bother with international school just for her senior year unless it was absolutely necessary.
A language program through the uni where you teach sounds like your best bet. My feeling is that the school will be fairly pleased with this arrangement. Teachers with kids are seen as more stable and you'll be bringing business to their program.
I would try and choose a school in either a 1st tier or a larger 2nd tier city that is well known for having a lot of foreigners. While most universities have language programs, in smaller cities those programs are going to be filled mostly with Asian students, and she may find that aside from the Chinese language barrier, she'd have a significant language barrier with her fellow students. If she's a typical teenager it will be important for her to have peers of roughly the same age, and especially in a new country, young people can have a really hard time adjusting if they feel too isolated.
Aside from the obvious Beijing and Shanghai, I'd look at cities like Chengdu, Kunming, Nanjing, Harbin, Guilin/Yangshuo and Xian. These are cities that often attract foreign students from Western countries, and, not coincidentally, also tend to be cities that attract tourists/visitors (not that they are necessarily tourist towns, but these cities have something to recommend them besides coal mines and factories). There are places, even larger 2nd tier cities, where people end up teaching but where no students would really choose to go and study. I would avoid cities like say, Taiyuan or Zhengzhou, for that reason.