Rhonda – this worked for me, too! iBooks was totally unresponsive on my iPas 3, with iOS 9.2.1. It had stuck showing the cover page of a book. Multiple hard and soft re-boots; opening and closing the app; altering its settings in ‘Settings’; nothing worked!
But, followed your approach of choosing to buy another book from iTunes, via Safari – in fact, the iPhone user guide, in my case – and I was able to get to a point, quite soon, where I could delete the errant book from my library and “from all devices” – and then the blockage just went away! Yay!!. I didn’t actually have to complete the download itself, in the end.
Thank you for taking the time to post! Your solution sorted my identical problem, too!