Thanks for that. Here's what I found out on your site. My plugin slideshow is using PrettyPhoto which is a clone from Lightbox. Same thing happens to your Pinterest Lightbox. Both are cloned from same source and have same functionality( or rather I say same method of displaying slideshow ).
Here's the problem. Pinterest Lightbox will be triggered on all images based on anchor tag that has image extension( jpeg, png etc.) without specific identifier, thus when you click on instagram photos, PL will run at the back of PrettyPhoto.
I don't know if you prefer this solution as it will break some functionality in my plugin but since your site has used to PL plugin, I think this will be the best option for you.
Simply Instagram will still display your images in widget but Pinterest Lightbox will take over on slideshow module.
Let me know how it works.