MIL Issues

So my daughter (3 months) wakes usually twice a night. She is breastfed & is usually back sleeping after 5-10 mins. My MIL insists that if I give her cereal she will sleep through the night. I’ve told her there’s no nutrition in it, & I would rather give her something that’s actually beneficial to her, not just a filler. What is everyone’s opinions on baby cereal? What are your experiences with it?