The planting seed is so true. I brought up mmf to her, lost her mind, fucked her later that night and she was gushing from having to think of it. It opened the doorWhen you wake up in the morning, tell her that you had a wet dream about her being fucked by another man while you watched and you loved it.
She will probably tell you that you are mad, but I bet the next time you fuck her you will feel the different.
You just need to "plant the seed" and let it grow..