I'd give it a go then. You can have different rules for different dogs in the same house you know.....Just because one does something, doesn't necessarily mean the other has to. I mean, my lot all sleep on the sofas and on my bed, but the Guide Dog pups were only allowed on the floor or in their beds and for the most part, they were quite content with that arrangement.
Just start as you mean to go on, regardless of what your Mum lets her Dachsie get away with. :wink: