iCloud Keychain keeps your usernames and passwords updated across your approved devices. You can use this with Showbie as well to log in easily! Just keep in mind, if you're using keychain with multiple devices, it will automatically log you in to Showbie on another device as well.
If you'd prefer not to use iCloud Keychain, you can turn it off in your iPad settings.
To learn more about how iCloud Keychain works, check out this link!