Could there be something in my home causing liver damage to my dogs?

Actually - these are the dogs at my mom's house - one of which is my own sweet little dog which I left with my mom since I moved overseas. My dog fell ill with liver disease about 9 months ago, and she's been "cured" and has been much better since. A few weeks ago, another of my mom's dogs was diagnosed with liver failure as well. The vet didn't think she would live, but she has - and she's doing much much better today - it looks like she's going to stick around for a while! Thank Goodness! But this makes my mom and I wonder - is there something that could be causing the liver failure? Could it be the flea treatments? She uses frontline. But there are also 2 cats in the house, and I'm not sure what flea treatments the cats receive. She lives in Northern Idaho, near Canada - so it's cold and snowy there now, lots of pine trees and mountains. They are pomeranians, inside dogs. They have wood floors, hardly any carpet in the house. Mom keeps a very clean and tidy house. She says the dogs do try to get into the cat litter.... but we're scratching our heads - is there something we can do to prevent the liver failure???