TwentyTwelve child theme: Incorrect footer menu

I expect that the theme_location is “footer” not “Footer”. It is case sensitive. I just checked. If you use a bad theme_location wp_nav_menu will fallback to what looks like a page menu when I test it.

Edit:

Due to additional information in the question, the theme_location is footer-menu and not footer. If you look at the Codex page for register_nav_menus you will see that it takes “An associative array of menu location slugs (key) and descriptions (according value.” The array key is the menu location. That is the value you need.