Dog Started Peeing in Her Own Bed?

I have an American Bulldog female who is 4 and a half years old. She is fully house trained. I rescued her from cruelty. I have had her nearly 1 year now and she suddenly started to pee on her bed and stopped moaning to go out when my family and I are in the house with the dog in front of us. She has never done this before and always moaned to go out to the toilet before.

As I said I rescued her from cruelty because her old owner left her in the garden 24/7 and starved her and used her for a punching bag. Since I got her she has learned loads of tricks, like sit and paw and walking off the lead.
Please can someone help me with the peeing as when she goes it stinks my whole living room out.
Thanks very much.