How would you deal with my mother-in-law?

My mother-in-law has a pet poodle that she takes with her wherever she goes - including to our home when she stays with us. Over the years I've had some concerns about hosting this dog in the same house as my young kids since he would display hostility toward them. So for a time, she wouldn't visit. Now the dog is aged - blind and deaf and doesn't react to anything - so he's harmless as a fly but it turns out he's incontinent. He's been incontinent on my bedroom rug, my new berber carpet in the basement, and who knows where else. . . When I caught MIL cleaning up after him on a recent visit she told me "it's no big deal. He does this all the time at home and I just clean it up". Now is it just me or would you not think that maybe I have some right to be upset? We are not pet owners, and if my own children had a pee on the rug I would be upset - let alone another persons' animal!! Likewise, if one of my kids had an accident on her rug, I wouldn't blow it off - I'd apologize and tell her I'd be sure that it wouldn't happen again. This is causing problems for me in terms of in-law relations and with the holidays coming up and the plans to host them at my house, I'm becoming less and less hospitable and it's affecting how I feel toward my MIL in general. How do I deal with this diplomatically?