Lightroom Mobile is an additional feature that can be installed on Apple IOS and android mobile devices to enable you to work on images on that mobile device. It was added in Lightroom 5.4. However, if you don't have a creative cloud subscription you won't be able to use Lightroom mobile. There is a little down arrow in the identity plate area that you can click on and you can pause Lightroom Mobile. Then you won't see that reference to it anymore. Lightroom Mobile is available in all versions since version 5.4. But if you pause it then it won't be part of anything that you do.
Lightroom Mobile is NOT the same as Lightroom 5.4, nor is it the same as Lightroom 5.7.1.
Lightroom Mobile is a new FEATURE added to Lightroom in Lightroom 5.4 and later versions, and is available to people who subscribe to the Creative Cloud.
If you have installed and are running Lightroom 5.7.1, then you have the most recent version of Lightroom 5. The only upgrade is to purchase Lightroom 6/Lightroom CC
Thank you Jim and dj_paige for your fast replies. I've been doing this reinstall with Microsoft tech support going on 15 hours, so I'm a little parched. When I first clicked on the identity plate it would not offer "Lightroom" or the ability to personalize the ID plate. It does work now When I first clicked on help, I saw Lightroom Mobile at the top, panicked, and didn't notice 5.7.1 at the bottom of the help box. Believe me the ID plate option wasn't workin'.