Big Paws Only Dog Forums

I bought a 2 year old female Mastif about 6 weeks ago.  I was told she was house trained, but at night, she frequently finds a nice piece of carpet to leave ginormous gifts.  I have tried confining her, with a child gate, in our master bedroom.  The doorway is right near our bed, so she isn't alone, but she whines a LOT.  Especially in the wee hours of the night, until one of us gets up and leads her to the backyard. 

I need advice on how to proceed.  Any tips would be extremely appreciated.

Brandy