Ah, now I get where it is. We're good now.
That one's tricky.
If you look at line 92 of
wp-content/themes/twentyeleven/functions.php you'll see this
// Load up our theme options page and related code.
require( get_template_directory() . '/inc/theme-options.php' );
get_template_directory() returns the theme directory or the parent theme directory. It doesn't return the child_theme directory so yes, that copy is always loaded from the parent and not the child.
Which I'm sure you know already, I'm just on one cup of coffee right now. ;)
The only advice I can think of is to try to filter it via
add_filter( 'twentyeleven_theme_options_render_page' , 'your_function' );
And see if you can append or modify it via Konstantin's example in the link I provided.