OK, I figured this out. I didn't understand what you were saying. I know you explained it in another thread, and I didn't understand it there, either. So I'll post the solution here, in case anyone else has the same problem.
OK, so: if you are in the category archive (category.php), $cat and $category_name are built-in. you can do
<? echo $cat; ?> and get the ID of the category you're on. $category_name returns the slug.
So, if you want a gallery of all your images in a given category, on the category archives, you just query the category and define it, like so:
<? echo do_shortcode('[mla_gallery category_name="'. $category_name .'"]')?>
You can also do:
<? echo do_shortcode('[mla_gallery cat="'. $cat .'"]')?>
Whichever you use, make sure it's symmetrical and you use the same parameter twice.
Thanks for the help!