But is this truly the situation where a union makes a difference? She hasn't been fired unfairly for someone who is a senior manager. She has ready employment possibilities and won't experience any hardship.

I'd rather they kept their powder dry to protect employees fired for things like union organisation, and protecting the workforce during large layoffs/reorgs, individuals discriminated against for their race/religion/sexuality, being compelled to take actions that are immoral/illegal etc. None of which seem to apply here.