MIL's house is too dirty

My baby is almost 2 weeks old and this is not an issue...yet. I know that eventually my MIL is going to want to keep our baby because she's already mentioned it. There's one big problem though--her house is disgusting. My boyfriend and his parents are dog lovers and that's sweet. I like dogs too, but my cleanliness comes first. My MIL's house is awful, to the point that I never go over there because it's so bad. Her carpet is soaked and stained with dog urine and poop. Her kitchen is piled up and there's always nats flying everywhere. She has 2 dogs and a cat, and 80% of the time she babysits her daughter's husky dog that's ridiculously hairy. All dogs are allowed on the furniture, therefore it's covered in hair and stinks because they rarely give their dogs bathes. I could go on and on...

I don't want to hurt her feelings or my boyfriend's feelings, but I seriously don't want my baby staying there. What about when she starts crawling around or picking up stuff off the floor? Anytime I've ever been there, there's at least 4 piles of poop on the floor. Her home just isn't sanitary at all. Is there anyway that I can approach this in a polite way? How do I voice my concerns without hurting her feelings? 

I was hoping (not expecting) that she would eventually deep clean her home but I doubt that will happen. 😞