How to Extract Label of a Field, which is inside FieldCollection?
This should do it:

$entity_type = 'field_collection_item';
$bundle_name = 'field_some_field'; // Field name the collection is attached to
$field_name = 'field_some_other_field'; // Field name within the field collection

$info = field_info_instance($entity_type, $field_name, $bundle_name);

if ($info) {
  $label = $info['label'];
}