Better Day does not collect any personal information.
The app contains no analytics whatsoever and no third party libraries.
In addition to collecting no personal data, Better Day makes no connections to the Internet, and as such cannot transmit data anywhere.
If you've explicitly opted in to diagnostic data sharing with Apple and third-party developers, Apple may share your anonymized crash logs with the developer of Better Day. These logs contain documentation about how the app crashed on your device, but no personally identifying information.
Bottom line: in the broadest of strokes, the developer of Better Day doesn't want to have your personal data, and avoids collecting it to the greatest degree possible.