I can match your problem & raise you one!!!! We too have poo issues in our household with our 2.5yr old. Oddly enough I also have a second daughter who's 9mths old. Our 2.5yr old is toilet trained but for the past 3mths she's been periodically painting her new room (we've just got an extension) with poo. It's so disappointing cleaning her hair, body, floor, walls, bed linen, toys, curtains & door. Her favourite thing to 'paint' is her bedroom door. I'm soooooo very thankful that we have polished floors, maybe you'll need to consider putting them in as they make cleaning a whole lot easier.
I can truly sympathise with you & the worst is that it comes out of the blue. My husband has been physically ill himself when helping to clean it up too. I try to look at what might be upsetting her at the time as I'm positive it's an attenting seeking devise. Most children don't care whether it's positive or negative attention at this age, they just want it.
I've also started getting my daughter to help clean it up. I know it sounds rediculious but she stopped doing it once she helped me wipe down the walls. It's so very hard not to get upset as it breaks your heart trying to work out why they're doing it. Luckily we haven't had an 'episode' in a couple of weeks (touch wood) & hopefully she'll have forgotten all about doing it.
Best of luck,
Peta, NSW, mum of 2 gorgeous girls