I think your best bet is to buy a long red wig to start with and use foam and / or chicken wire like suggested.
Since this material is pretty light, you can use counter-weight
to help keep it on your head as well as clips instead of relying on clips to hold it on by sheer gripping power.
Also, from an aesthetic standpoint, I think you're much
better off building her hair out to the side / back, instead of straight back. Her hair is often shown to the side, and I hate to say it, but it looks kind of silly going straight back, especially on a real person - it means you can hardly see it most of the time, which makes a really, really, weird look. I think going to the side would create a more true-to-character look.