Tough Cookie is the 9th in the Goldy Schulz series by Diane Mott Davidson. It has dropped to £0.99 at Kindle UK. Titles in this series only rarely go on sale, so if you are lucky enough to live in the UK, or can travel there, grab it if you want it.
link:
https://www.amazon.co.uk/dp/B07M7WBNQ8