Let me restate your issue to make sure I understand it. You posted a link to your "Portfolio" page. When I click on any of the images on this page I go to a page that should show the individual image in full size. The images for galleries like "Yosemite" work correctly, but the images in the "MLA Gallery" show a thumbnail size image.
It looks like the single-image pages for galleries like "Yosemite" are composed with some shadowbox shortcode/plugin, but the images in the single-image pages for "MLA Gallery" are composed with [mla_gallery]. If that's right, I think the solution is to add size=full to the [mla_gallery] shortcode. Here's the relevant section of the MLA documentation:
The Size parameter specifies the image size to use for the thumbnail display. Valid values include "thumbnail", "medium", "large", "full" and any additional image size that was registered with add_image_size(). The default value is "thumbnail". You can use "none" or "" to suppress thumbnail display and substitute the item title string for the image/icon.
The [mla_gallery] shortcode supports an additional Size value, "icon", which shows a 60x60 pixel thumbnail for image items and an appropriate icon for non-image items such as PDF or text files.
If I've misunderstood the issue or that's not the answer, having a look at the page source code would be helpful. Let me know if you need more help with this issue.