Any way to force an app to rotate?
You might try the Ultimate Rotation Control app -- when I tested, I found that it could force any of the apps I tested to rotate.   It's a seven day free trial, then requires a license purchase (US$2.99).

It turned out that I didn't really consider the app that inspired me to download this any better when force rotated, so I did not purchase, but your mileage may vary.