Chachi - I think you and your SIL should first go out and buy something for MIL's house, take it over to her, expect her to pay for it. Then, you and SIL should redecorate one of her rooms while she is away. You can explain to your husband it is simply an "empathy-building exercise". Perhaps she will learn to have empathy towards her DILs if she knows how they feel.
I would have a HUGE fit if my MIL redid one of my rooms in my house behind my back.
