How do I get my cat to stop pooping everywhere?

My cat is very sweet but seems to have this evil streak. She recently lost her buddy (my other cat passed away this summer) and of late, whenever I am away from home for more than 12 hrs (I work a lot) she leaves me little poops everywhere – except in her litter box.
I’m certain that she is lonely and this is her way of letting me know that she doesn’t like it when I’m not home but this is unacceptable. When I am home we hang out a lot and she gets lots of love.
Her litter box is clean and easily accessible and I haven’t changed her routine at all (she used to use it) but now she just doesn’t use it at all. Who knows where she’s even peeing…
Besides me not leaving my house or getting her a friend, how do I stop her from pooing all over my place and return to using her litter box?