Honestly, I am not sure she could defeat Jean alone if she didn't act immediately. Determining the victor in a battle between Jean and Wanda would really depend on timing. As I noted, if Jean acted first using her telepathy, I firmly believe she would incapacitate Wanda. This is not to say that she would, but Jean could even use her telekinesis afterward to lobotomize her.
However, even if Wanda acted first using her chaos magic, I wonder if Jean could still subvert her efforts telepathically, perhaps forcing her to invert her hex(es) or turn them toward something or someone else.