I love in-law questions.
They all have the same running theme, we mothers are always unable to communicate with them, what we need from them regarding OUR children. We've all had these same issues.
My advice to you is that its not worth it to get stressed over things you think theyre going to...
If she's exclusively breastfeeding, and not expressing her milk to bottle feed either, and baby is still feeding during the night, then its highly unlikely but there is always a tiny possibility.