Growling and barking puppy..help?

We got a 8 week old lhasa apso bichon frise cross puppy last week, she was perfect the first few days and we loved her to pieces, then 3 days ago she turned nasty and growls at me and partner, ie when she wants to get on sofa or when we put her in her play pen. Sometimes she will even start growling just when we are looking at her. We try and discipline her, tellng her NO and ignoring it and have banned her from the sofa, yet she seems to be getting worse and has started to bark as well as growling. We really are at a loss of what to do now as we love her but can't cope with an aggressive dog.