I think you need to explain to your wife that training takes TIME. No behavioural issue will disappear overnight. As Lexi seems to prefer softer surfaces, you could look at getting some cheap fleece blankets and wrapping the sisal posts in them. We have also used folded fleeces to protect furniture when we have a new cat (or new furniture! New pieces always seem more tempting ). Another option would be using carpet remnants to wrap around furniture legs/corners to protect them. Carpet can make a great scratching post surface too.
She WILL learn where not to scratch in time - you just need to stay patient.
She WILL learn where not to scratch in time - you just need to stay patient.