Hi there. I am presuming that she is urinating rather than defecating in this room.
When cats start to do this, it's usually because they are annoyed or upset about something, and this is there way of expressing it!
The first thing you need to do is get a proper 'odor eliminator' product from the pet store, that will destroy the odor of the cat pee in the baseboards- normal cleaning products don't work, and if she can detect any remnant of urine she will keep using the same place again and again. Any products containing bleach actually make it worse!
The other thing to do is get a 'Feliway diffuser' this is a plug in product that releases 'happy cat' pheromones into the air, it's very useful for treating a lot of cat behavior problems, but especially marking problems. You should plug it in in the problem room.
If you can pinpoint any cause of stress, then obviously try and remove it. Failing all that, drug therapy can be an option, but do try and exhaust all other routes first.
Andrea
Cat Veterinarian
bvm&s degree, 15 years of companion animal practise