Gross!

My dog has been doing really well with the potty training thing. We've had over 2 weeks with no accidents in the house. She was even starting to come and tell me when she needed to go out. Then, this weekend, she went in the house 4 times!! The last straw was this morning, she pooped on Aiden's bed. Luckily he wasn't in it at the time, but how NASTY is that!!?? I stripped the sheets this morning, and when I get home I'm going to sanitize the mattress. I'm so grossed out right now. I yelled at her and put her outside so that I wouldn't be tempted to beat her to death. I just don't know what's going with her? Why is she all of a sudden doing this? I'm letting her out just as often as I always have, and the routine has not changed. I don't understand. And she knows she's been bad, because she will go hide after she's done it. So I know she knows better. I'm just really frustrated with her and totally grossed out. Any ideas?