Change Index Gallery Layout Grid to Slideshow for mobile

Hi there --  I have a client who would like some adjustment to her mobile view. She likes the index gallery grid for three images for desktop and tablet, but on mobile the stack creates a bad intro to the site. She asked for it to be three images on the same row for mobile too. 

I tried targeting the image gallery for a max width of 33% but that just reduces the image -- they stay in a stack. Any way to remove the stack for tablet view? 

I'm wondering if she won't like this solve for mobile. I'm wondering if there's a way to create a media query to change the index gallery layout from grid to slideshow just for screens at 640px. 

Anyone got a solve for this? 

Site is heatheretheridge.com/welcome and it's the first index. 

#home-gallery

Thanks for looking. 🙂

Lacey