Can't get child theme to overwrite a parent theme's template file

Ive been customizing a FlexiThemes theme with a child theme. I’ve been able to make modifications in many of the root folder files (style.css, header.php, functions.php, etc.). But I now need to make a modification to one of FlexiTheme’s own widgets (I need it to return a custom taxonomy for each post on the sidebar widget).

I know the code that I need to use (and have in fact got it to work when I make the change on the parent theme’s file), but when I try to add the modified template file onto my child theme, nothing happens.

I’m assuming that the problem lies on how the widget file is called by the parent theme. Here’s the location of the file:

parenttheme/flexipanel/widget/posts.php

The parent’s functions.php file has this bit on it:

require_once TEMPLATEPATH . ‘/flexipanel/FlexiTheme.php’;
$theme = new FlexiTheme();
$theme->theme_name = ‘TheNews’;

Is there a way to overwrite that on my child theme? Because I’m assuming that’s the problem.

The /flexipanel/FlexiTheme.php file has a bunch of TEMPLATEPATH. lines too.

I’ve already tried to copy the entire ‘flexipanel’ folder (with the modified posts.php file) onto the root of my child theme and it didn’t work.

Any ideas what I should try next?

Thanks!