i am just a little confused. you didn't really say if you were planning on re-decorating. If you are,then whe not give her some specifics of what your looking for. Or go shopping with her.
If we really were planning on redecorating and you and your husband are happy the way it is, then you both need to just tell her that "it's a great offer, but we really don't want to redecorate right now." If your MIL was offering after one of you saying something about doing it, she should understand. If she was offering because she just doesn't prefer how it's done, then that's selfish on her part.
Maybe if you weren't planning on making changes you could have her help you reorganize things