So bringig traffic to the blog is a big value, so she should pay for this service. But she doesn't, because search engines are free.
News sites can block google and other bots any time on their sites with robots.txt, but they don't because they want the traffic for free, while they even demand money from those who bring the traffic.
I was feeling different about this topic until you brought this up. I think this is a really good argument. Yes, google scrapes and gets value from what they scrape without paying, however you can block this as a publisher if you don't want this.
You do have a choice though. You can choose not to use google ads and stop performing SEO and drive business in alternative ways. Further, there are more search engines than just google. If your business model depends on google it may be time to rethink that strategy. Any competent marketing strategy would rely on diversified channels anyway.
A comparable scenario would be something like the phone book or yelp where these directories have value to users but they simply refer users to the businesses advertising in the directory.